Nope, a single card(ATI or nVidia) will work fine with any processor(AMD or Intel) its just that dual card setups require specific chipsets and there are no good chipsets for AMD CPUs that support SLI.
They couldn't get away with that.
Some time ago I wondered the same thing when I had an ATi R420 chipset and I wanted to use my Nvidia 7600GT.
Everything agreed and there was no war with the camps involved so I suppose a truce is in effect as long as it's just a chipset.
Careful about those chipset drivers in the 'add/remove programs' list though...they may be a bit fickle if uninstalled.