Lucy Spell Details reveal the push back caused by spell casts. A 'pushback' of 1 will move a mob 1 ft in-game.
Click on the spell to be directed to the referenced lucy spell info:
1. Bolt of Molten Scoria Rk. III: Pushback = 0
2. Shock of Discordant Steel Rk. III: Pushback = 0.5
3. Beam of Molten Scoria Rk. III: Pushback = 0
4. Jolt of Many Rk. III: Pushback = 0
5. Annihilate the Anomalous Rk. III: Pushback = 0
6. Torrid Sands Rk. III: Pushback = 0
7. Fickle Blaze Rk. III: Pushback = 0
If I can find the pushback values per melee hit, I will post them. But for now: summoned pets use hand to hand unless they are given a weapon. The weapon a pet holds will determine what melee skill it uses. I suspect melee push values for each melee skill type need to be determined through controlled observation.