TBH i don't know, though i think so.  the whole idea that the endpoint you connect to depends on your auth identity seems weird to me, when everyone else has a standard endpoint as it already knows who you are.

however it does appear that when google constructs an identifier email address it uses `#####-lettersAnd###@developer.gserviceaccount.com` where the first ###### *is* the project id and the subequent lettersAnd### is some sort of randomly generated uid (and it's this last bit which may be new from GCE but which we certainly should not be using to construct the endpoint!)