Isn't that pretty much the definition of eDRAM?
In most cases yes, but the eDRAM for the XBox360's GPU was on a separate die, so that's a potential case for the Wii U as well.
Also it's unlikely that it will be used for GPGPU stuff as access from the CPU will likely be much slower than main ram, if it's even possible
As Blu says, due to BC requirements, the eDRAM has to provide the same sort of access for the CPU as the 1T-SRAM did for the GC and Wii. Basically, we're probably looking at these sorts of characteristics for access to the eDRAM:
CPU: High bandwidth, very low latency
GPU: Very high bandwidth, extremely low latency
Which conforms pretty well with what you'd need for a GPGPU scratchpad.