From what I can tell, in theory, yes, but it seems to be kludgy..
You should be able to go to the Transpose Track and transpose the entire song from there. Of course MIDI (Instrument) tracks will follow any transposition setting, as will Apple Loops, and supposedly if you have Follow Tempo & Pitch enabled so will audio tracks. But I couldn't get audio tracks to follow the Transpose track. (Maybe I missed something?)
However if you're just doing a static transposition of the entire song, it should be easy enough to enable Follow Tempo & Pitch for all audio regions and manually transpose them to match. Be forewarned, thoughâ€”the pitch transpose quality in GB seems to be nowhere near as good as Flex Pitch in Logic, and the rhythm seems to suffer glitches here & there when pitch-transposing. But I guess it's worth a try..