Didn't all the alien actors in AVATAR wear these types of suits for their performances in that movie? It was not just one guy doing it for all of them - hence anyone can wear it.
Certain fx companies get a comfortable working relationship with a specific performer and tend to go back to them for these sorts of things because they already know him, know what his limitations are, etc. Rick Baker has used John Alexander for years for his apes and aliens [Gorillas in the Mist, MIB, Mighty Joe Young, etc.]; WETA has uses Andy for all their stuff [LoR, Kong, Apes, etc.]; this is how Doug Jones got the part for Abe in Hellboy - the effects shop suggested him.