There were a FEW harems where there was a full-time muzzayyina employed. 

However, in every instance I have found documentation on,  the henna artist was on a pretty low rung of the social ladder, with  the potters, barbers, cobblers, weavers,seamstresses, and other  self-employed artisans.   Or they were a member of the family, (and that  was different).   Within the family group, you had your status by birth or marriage, 
and the effections or esteem that went with the relationships in that group.  If you were just hired for the job, and were a stranger or acquaintence coming in  .... you entered by the back door with the rest of the tradesmen.

Indian henna artists, women of the Nai caste, brought to the finest princely households,  were given a silver wire with which to apply their henna, and allowed  to keep the wire, or might be paid with a new blouse (choli).  

In  Spain, the henna artists were frequently Sufis, who embraced poverty  as worthy and spiritually excellent, and were on the poorer part of the income tax collector's route. 

In North Africa, the transient women who did female  circumcisions, tattooing, entertaining, fortuntelling, and suchlike also might also do henna. 

I   haven't, so far, found any instance that it was a highly regarded  profession (in  social status) ...because you were a woman  (perhaps an entertainer)  who went about to anyone's house, and worked  with the soles of the client's feet 
(unclean and generally defiling to touch, in many groups).

Now, some of the full time hairdressers and henna artists were brilliant, don't  get me wrong, ... they were just usually of a fairly low social order.  Generally speaking .... as far as I've found, the henna artist in history was  right up there with the hairdresser and acrylic fingernail lady, and one step above the washerwoman.  She might have been  regarded fondly,  even a trusted confidante and go-between,  but not a  debutante in the cotillion ball!

If you were a member of your clan, and happened to have a knack for drawing, doing henna for your family didn't raise or lower your status within the group.   The younger wives in the houseolds were generally assigned to do the henna application in traditional India, and the older women to pounding and preparing the henna.  The prettifying was considered more appropriate to the slightly bored giggly subordinates.  The grinding and mixing was done by the more experienced hand. If you were known to be the local  girl who had a steady henna line and a way with pattern .... your skill could be well recieved,   and you could have status in your group .... but that was NOT the same as doing "henna for hire" as an independant craftsman. That was based  on your status within the family, and not because someone was paying you to  sling henna . 

In 19th century Morocco, a young girl named "Fatima" was the most auspicious choice for the wedding henna artist for the bride, and a young boy named "Mohammed" was the luckiest choice the men's night of the henna.

Who's working today?

The henna artists that I know about in India, Sudan, Egypt, etc ...  these are still working ladies about on the level of a highly esteemed  hairdresser, or clothing designer and seamstress. Some of the ladies   in India have wonderful companies where teams of them maintain very    high standards of henna and work together to do the massive society  wedding gigs. They're highly valued, but I don't see that they have  social standing higher than the caterer or entertainers.

Will henna ever be "fine art"?

Using art to express one's own ideas is very, very recent ..... mostly  art has served a function of making one's environment more enjoyable  to live in, or to be instructive to the illiterate. The artist mostly  served the needs of the job at hand with what skills he'd learned.   Sometime around the 1800's there was a change in Euro/US attitudes   towards artists. Before that, artists were artisans/craftsmen ... and    they were working folk who did art for a living. They might, occasionally, get to hang out with the posh folk (like Da Vinci,  Michelangelo, Velazquez) but they were reminded regularly that they were  "hired help" and NOT "nobility". They were occasionally paid well, and  sometimes respected for their intellect ... but they, like Mozart,   just got to "play" with the upper crust, not "be" the upper crust.

When the middle class rose after the industrial revolution, and some  people had leisure time on their hands .... and economic times were easy enough that some people could support themselves as artists and  indulge their own whims a bit, not just knock out another commission   .... the notion of artists rose.   At first, the idea of greatness and revolutionary purpose was just    in the artists own fantasies (the French Impressionists and  and the Post-Pre-Raphaelites were good examples), and people thought  they were a half-mad stuck up lot who were drinking way too much and  living off the charity of their relatives. Then as their work became  valued (it certainly wasn't at first) the legend of "artist as social  commentator, intellectual and visionary" arose. This is an extremely  novel and recent notion ..... and largely due to the blossoming of  "art history" classes, public museums, and the middle class taking  college courses and endeavoring to become cultured.

If henna moves into to the newer definition westernized of art ....  highly intellectual, social commentary, serving one's own vision and   presenting it to posterity .... that will be interesting, but I don't see it happening presently. The henna artists I see working are still  pretty much in the artisan "serve the client's needs" mode.

 Since henna art is ephemeral, it's got only a limited potential for  that "self important" character of exhalted modern art.

Thank God for that!