It's clear that the perks are not spells. Thus, the steam tank can, RAW, be affected by them. I don't think there's any plausible argument here. (And the fire perk affects the tank, not the caster - it works for any fire mage IIRC).
Of course not, because a unit buff affects the unit buffed, not the unit it is fighting.
It obviously effects them both. Suddenly my steam tank is getting hit by S8 attacks thanks to the 'spell effect' of occams mind razor. Using your interpretation, that any 'spell effect' that affects the tank is verboten, so would buffs helping people fighting the tank.
My point about the T10 is because I think it's plausible that a steam tank that can be healed is a bit OP, thus I would not be surprised if there was an errata/FAQ changing it. If other T10 guys can be healed, then maybe GW is ok with it.