I'd like to know if there's any way to use a Wii guitar (drumset, etc.) on a PS3 - or a PS3 guitar on a Wii.
Do I need any adapters?
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.
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.
ANY Rock Band or Guitar Hero instrument that uses a dongle rather then a factory controller is interchangeable. Guitar hero controllers are harder to interchange then Harmonix, but not impossible. To use them on consoles other then originally designated requires soldering. Harmonix instruments simply have a jumper near the microcontroller to determine which system the instrument is for. This is true with ALL HARMONIX. Possibly those Red Octane controllers using a dongle as well. The simple fact is, if you search the web, everyone says no, not interchangeable, they don't speak the same language, bla bla. While this is true for non-dongle GUITAR HERO controllers, it is not for ROCK BAND, and those with a dongle. Here's why. The dongles were not made by Nintendo, Sony, or Microsoft. They were made by Harmonix and/or Red Octane. Therefore, they are not proprietary and unique to each system, and DO speak the same language across the board. The instruments that used the factory controller(wiimote, sixaxxis, xbox) to interface with the console generally are not really interchanged. Open a Harmonix controller, and look for a bubble of solder near the edge of the board labeled J1 - J1.5. Bridging one side is ps3, bridging the other is Wii. That simple! If you have any questions, send me an email. Bumbarg.j2@Gmail.com.
Since all peripherals use USB to connect to the consoles you should be able to use Wii guitars etc on PS3 without adapters. I've done it myself with a mate's Wii guitar to play PS3 Guitar Hero.