Honest, straight up answer?
Legally, I'm not a lawyer, so I can't speak on the legality of things. I can tell you that ripping music from commercial games is generally a pretty safe venture if you're not trying to sell your own game for profit. People have been using music from commercial sources for all kinds of things for years without any sort of scrutiny. If Wiz Khalifa can use Schala's Theme from Chrono Trigger in a song, you can generally bet you won't go to GAMER JAIL (or a C&D, rather) for using some Wild Arms theme in your own game.
Using music from a small time indie developer without credit is generally a moral no-no since they're fellow artists of the same kind and they're far easier to go ahead and contact to ask for permission, so go ahead and do that.
From a strictly entertainment point of view, generally in my experience as a consumer, most people don't really care as long as they don't NOTICE. So hearing the FFVII boss theme is likely to snap the player out of the game, because well, so many people recognize that tune. However lesser known themes will usually get a 'hey I remember this song from...some game or something. Oh well, moving on!" at best.