I haven't yet, came across a FAA artist using another FAA member's work.
However, I have within the past few months came across a photographer's website, who has stolen another photographer's images. I was able to track down the original photographer and notified them. They contacted the one who stole the images. Although the images were removed, the photographer who stolen them.... she stole more images, from different photographers. Once again, I was able to track down the original photographers and I contacted every single one. It got to the point, that the photographer who stole, made a blog, telling people to stop contacting her about removing the images.
I've blog about this photographer. Here, you can read all about. http://crystalwightman.com/cmjvphotography-stealing/
I actually made 3 blogs about her, on 3 separate incidents.
About a month ago, a woman emailed me, letting me know, the said photographer was in a facebook group asking for advice when someone keeps blogging about her. :) Of course, there were answers about suing. No one in this facebook group knew what the blogging was about. No one knew, she has been stealing, using other photographers pictures on her website.
So, with that being said. If I come across another FAA artist using another FAA artists work. I will contact that original artist and let them deal with it.