The behavior in wellington does not literally seem to be that its using the same mechanism as pvp off though- pvp can still be on in wellington but something else prevents you from hitting people and structures there. It’s not a scenario in which pvp off is forced upon the player, if your pvp is on in wellington then logically you should still be able to hit your dog, and the same would apply to everyone else hitting your dog.
outside of wellington compare this concept to walls, with pvp off its an obstacle, with pvp on I can eventually tear it down. that doesn’t mean its not a wall. and being able to hit or not hit a dog does not put it in the same category as another player.
I haven’t confirmed whether or not you can hit your dog (neither has the poster) but I can certainly try later