Minions can do critical hits (100% additional damage).
Minions get the attack value either from owner or caster. Most of the time caster (= Kvasir). Like DoT (fire, poison) only the base value counts. So a temporary attack increase (Boldtusk, C.Kailani etc.) is ignored for DoT and minions.
The troop bonus still affects minions and DoT. So leveling troops for a higher attack value will increase the damage of minions.