Channel WAD's are just fine.
VC and WiiWare should work fine, even injected stuff (as long as it worked on the Wii)
Forwarder channels have to be the new vWii compatible forwarders but even an old one won't brick anything. It just won't forward.
I don't think embedded homebrew channels work ("full" channels as some people call them) but I might be wrong and again they won't brick anything. They just might not run.
Just don't install a WAD of a theme, system menu, IOS, BC, cIOS, MIOS, DM(L) or any of that system stuff. They could be a bit more dangerous to your system.