Not quite. Wayland itself doesn't require any graphics-driver-specific code; it uses the standard kernel interfaces and graphics stack (Mesa, DRI, libdrm, KMS, etc). That also works fine with radeon and nouveau, and it would work fine with the proprietary drivers as long as they support the standard graphics stack. It just won't work with proprietary drivers that implement their own entirely un-integrated graphics stack, which seems unsurprising to me.
Your window manager of choice can just link into Wayland/Weston and ignore all the underlying graphics driver bits; they'll Just Work.
It's been years and years since I knew the details, but at one point the nvidia drivers replaced pretty everything from libX11 down, and I don't think you could hook in at a middle point. (ie, they don't support the "standard" graphics stack.) Would appreciate if anyone could comment on how things stand today.
Somewhat better, but still awful. They don't replace libX11, but they do replace libGL, and they bypass the entire kernel graphics stack in favor of their own.
Your window manager of choice can just link into Wayland/Weston and ignore all the underlying graphics driver bits; they'll Just Work.