I've mixed and matched a little bit for one reason or another.
I do have to watch it a bit at my favorite used bike store that they'll sell a 175 and a 170 as a pair.
As mentioned, most cranks have the diamond orientation, but some don't. If the bottom brackets are pretty standard, then clearance shouldn't be an issue.
Personally I would avoid replacing a black crank with a silver one, or one with a fat arm with a narrow arm, but that is more aesthetics than anything else.