Yep — regarding spells of various schools, cost or in general. Destroying minions doesn’t seem to get credited anymore either, however, playing minions — just minions in general, not of a specific type (I think I could confirm your report about this, but I’m not sure and could be wrong) — apparently does for those mercs abilities that are more ‘minions’ than ‘abilities’ (see the quoted bug below), e.g. Beastly Beauty, Bladehand Berserker etc — you could also recognise these by a distinct frame.
Probably not. Regarging the first part of your question, that is — I’m quite positive about that, and as for the second — hard to say. They have intentionally ‘nerfed’ XP farming in Mercs, from what I recall, so they might have also closed this opportunity to do some quests in an otherwise forgotten mode — or it was another side effect.