Using a Wii/PS3 guitar heroes guitar on a PS3/Wii console

Solution 1:

For the wireless controllers, there's no cross compatibility between consoles. Each console uses a specific protocol to connect, and they don't talk to each other.

For USB wired controllers, it's likely possible with a 3rd party adapter, but each controller has console-specific buttons, so I don't know how that would work exactly. For instance, my Xbox drum set has an "Xbox" button on the face of it.

Heck, the Wii Guitar Hero World Tour drums and guitar don't even work with Rock Band on the Wii - getting them to work with another console's games is right out.

As you pointed out (?) there's a Datel adapter available that adapts the Wii Guitar Hero Guitar (supposedly) to RockBand on the Wii and on the PS3, but people have had very mixed to negative results with it.

Solution 2:

Although I don't know of a way to use PS# guitar on Wii and vice versa, I was able to use a a wired Guitar Hero guitar for the PS2, the one that came with the first Guitar Hero, on both the PS3 and Wii, though both require adapters.

I have used this adapter for the PS3 and this adapter for the Wii, though I'm pretty sure there are other compatible adapters.