I have the CE of Doom3 for Xbox. There is no no-clip cheat on that version, and that means no Romero-head.

What about the XBLA, is there noclip there so we can saw on John's head?

There are no cheats for XBLA Doom, but presumably Johnny's head is still there as it would be more trouble to take it out of the game than to just leave it buried in the game's data files.