I retried and no matter what it didn't trigger. Another test with a different char, another build, no raven. Therefore i wonder if there is something on my TQ installation that would impede a pet proc, but i have only Xmax and a texture mod installed. And with the chest Megingjord item, the wisp is well summoned on attack.
Even if it's merely cosmetic, the raven may be useful with a diviner. There is a mana cycle: mana drops to 0 and is refilled quickly with dark covenant. And pets damage is boosted by the nightmare aura.