AMD wouldn't care if those memory chips are used for intel or nVidia GPU's or any other brand. In fact before intel's Pentium II CPU you had 1 socket (mainboard and chipset) for any x86 CPU.
If you want to design a cpu for AM3, or whatever AMD socket, you can do that without a problem. To be even more accurate, if nVidia really did design a CPU it will most probably be a AMD socket CPU.
Hypertransport for example can be used by anyone who'd like to use it. So I don't think AMD would tell manufactures where they can and can't use those memory chips. And besides, I've had enough mainboards for AMD cpu with intel branded chips on it. So I don't get the big deal here.

