Many things to say here. First... the decomp project only decompile to x86 platforms due to the intrinsics , so it will not work straight up with the Wii U since it's PPC.
Second, the generated code is not aimed to be human-readable. so it will be an even bigger pain in the ass to port it.
Third, on Wii U you have the GX2 API to learn in order to use this, so there is that too, if you want the best performance you will need to use the proprietary API (the SDK mentioned that it was based on OpenGL, but I don't remember how similar to it was). Anyway, XenosRecomp recompiles to HLSL, which can be used for Vulkan and DX, but neither works on the Wii U.
And finally, about the CPU, the Wii U CPU is overall more or less on par with the Xbox 360, perhaps slightly more powerful even, since it has a far better IPC, the logic processing of it is much better than X360 (which is the most important thing on a processor).
It's not exactly a PowerPC 750 because it has features that a PPC750 couldn't have (SMP support, 1GHz+ clock speeds...), but it's 100% binary compatible with it. The reason for the "slow" speed of the CPU is because it has a very short pipeline, but it's extremely efficient, if you have a cache miss, the penalty is lower thanks to the shorter pipeline, has FAR lower latency than the X360's CPU to memory, far more cache, OoOE, etc. It just sucks at floating point arithmetic, which many games on the 7th gen were optimized for, but it's better than the 360 at everything else.
It's a bit late here and I feel like I'm forgetting to write something, but eh, guess that's pretty much what I wanted to write.