Yes it's true, Nobuo Uematsu has retired from Square Enix. It seems that he may still help with upcoming games, but for probably about 1% of the games (My estimate). If you want proof, here it is!

Clicky

he didn't retire. He just moved on to start his own company, now that he is famous enough because of the games. He said he also liked the songs he made for the FF games. And even though he is now a freelancer, he will probably work some for his love of the SE games. He just feels overworked, that is why he doesn't want to work under SE. If he doesn't work for them, then he only needs to compose for what he feels like, not everything they tell him...