The GCM IV thing didn't ring true to me either; in fact, the whole reason we have XAES-type constructions is to enable fully nondeterministic IVs, which don't fit comfortably in the GCM IV space.
Regarding padding oracles: it is most definitely not necessary for a target to generate a "padding error", or even an explicit error of any sort, to enable the attack.
Regarding padding oracles: it is most definitely not necessary for a target to generate a "padding error", or even an explicit error of any sort, to enable the attack.