So if I assign a devotion ability a summon...

does it get the benefit of my +pet stats when it procs? I know my pet will proc it on attack, but is it actually using my pets super boosted stats for damage and such?

I believe so. why wouldn’t it?

sidenote, if the devotion allows for the pet in the devotion calc of grim calc then the skills that will proc it is also listed(sometimes the pet skills are listed, without the pet, so thats meaningless and can be ignored)

From the Game Guide:

Celestial Powers
[…] Note that when you assign a Celestial Power to a Pet Summon skill, the power will be triggered by your pet instead of you and will scale with any bonuses that normally affect your pets. […]