Considering both game will be run on a very similar gaming engine and Activision/Neversoft are working hard at cross-compatabiliy even with rivaling gaming companies (ie. Rockband) it is safe to say yes. For the Xbox 360 everything through the Guitar Hero franchise has been compatible. The majority of problems only came into play with the Wii and Ps2 if i recall but you can assume that Guitar Hero World tour and Guitar hero 5 will be completely compatible on all systems as they will be quite similar.
Yes they will work
yes
Yes the guitar hero world tour (4) controller will work with guitar hero 3 on any system
yes
yes
Yes, It should.
I think they only work with Guitar Hero 4
http://www.rockband.com/compatibilityWill answer all your compatibility questions.
Guitar Hero World Tour is Guitar Hero 4.
It does work for other games, at least for 4 and 6, anyway.
yes it can work for any guitar heros unless one is for the 360 and one is for the wii
no, for some reason rock band stuff [drums,guitar,etc.] do not work for guitar hero but guitar hero stuff does work for rock band.