It does effect it some but not the full amount stated by the spell after using Vampiric.Have recast buffs resummoned pet and is not the full amount for Necro scout pet
I do not think the new Vampiric Requiem has any pareseable effect on the summoners primary pets (maybe someone with a new rune can test it) That's what purple panda VR rune does: Looking on the visible pet stats +19,55 VR makes 1000 potency / 20 CB and some health/resistance, but this has no infuence on the dps of the pet. And YES, VR has big influence on all summoner's mitigation buffs - That's the reason it makes sense wearing it
So tested again with the Zimaran Rune: Nilborien's Vampiric Requiem (20,94%) and recasted pet No measurable difference in DPS of the primary pets (10 min test against trining dummy, pet only) This might be a bug, but it's in the game forever. As mentioned summoners mitigation buffs get the 20% boost. The boost is persistent until zoning/death.
You must recast the spells not the pet and there is a difference in before and after it is slight but there.