A: as the restriction of the HD are included on the Target entry for Daze, and it is not included in Mass Daze, if not errat'd, I would consider it to affect any HD number, and the only restriction is the distance between targets. Anyway, do not expect to Daze 100 enemies with it, you won't get a clustered block of enemies if you are not fighting roman legion.
B: I would say it is not. Again, spells do what they say they do. But the spell still is a Compulsion, Mind-Affecting, Language-dependent one; so if the target is immune to spells, or to compulsions, or to mind-affecting effects or does not understand your language, then the spell still fails. So it is not that awesome as it might seem.
