I would, however, not at all be surprised at it having a direct connection to the GPU, either both hitting the same memory management hardware, or even so far as each being able to directly manage a shared cache, maybe even with the CPU being able to manipulate GPU register files.
Hitting the same MMU or whatnot is very possible (since that's how the 360 is), but it's rarely useful, if not downright harmful, to be able to directly manipulate the GPU's register files. The whole reason why the GPU can be so parallel and fast is because it's decoupled from the CPU. If the CPU has access to the GPU's register files, and this feature is "taken advantage of", then that means the CPU and GPU are both running in lockstep, which is terrible for performance on both ends (as in, they'll be spending 99% of their time syncing with each other).