And another opinion added.....
I don't envisage any problems at all, all computer componets should work well together providing they're designed to work on the same platform.
Any doubts are probably suggested by the Corporations that make the components as they have vested interests in selling their own product.
They obvioulsy want you to think only their products work well together so you give them your money.
It's a jungle out there
However, FWIW, I'd go with Nvidia graffix atm.
I was a big gameboy fan of ATI vid cards for years but the last card I used made by ATI was a 9800 Pro circa 02.
Since then, Nvidia have been good, very good. And Nvidia also supply good support for Linux Users whereas ATI do not. That is a big plus in my book.
But hey - it's your choice