Same as everyone else said any card combo will work (with compatible drivers and SDK)...
Just one exception in case you were wondering, they will work just fine for mining but don't expect to use them *together* for gaming. You will be able to use one of them if you want to play games, preferably the faster, but you won't be able to crossfire unmatched cards.
I have heard of rare cases that people got unmatched cards to work with driver and software mods but they all took a performance hit.
Just wanted to make sure you understood that part of it
Otherwise go for it, I've even mixed nvidia cards with amd before!