This is a makeup artist in Atlanta that really makes a big issue of this, but the reality of this industry is far different than she tends to project.
you asked if photographers only use licensed MUAs. How about I broaden your question a little and say this. No clients, catalog, magazine, or other have EVER me asked about this. It is not just photographers. I use the best MUA available.
I have heard the licensed MUA go on about how important a license is. This is great marketing on her part. The realities of this industry dictate otherwise. Mary Jane Starke, no doubt the most successful MUA in ATL, commanding the highest dayrate BY FAR and working a LOT, laughed when I mentioned the whole license thing to her. She talked about how how none of the top MUAs in the country are licensed.
If it is good enough for the top print magazines in the world, top photographers, and my paying clients it is good enough for me! The license thing is a nice to have, but don't let a chicken little scare you off with horror stories that may be good marketing stories when it comes right down to it. Reality is different than what can be presented. Some people make it sound as though that license means you are more sterile....lol.
Let me ask you this. If you have a licensed MUA that does not do as good of a job, or talks and talks while she is supposed to be doing makeup, vs an unlicensed MUA with monstrously large national tear sheet credits and does better work faster, who would you use?