Scorpid pets are tenacity pets. Tenacity pets have an okay tree, but not nearly as good as Ferocity for PvE and PvP. Scorpid Poision is a dot that does 100-130 damage, which scales with the pets attack power (much less than before, and it does not stack).
The major spell they bring as Tenacity is Roar of Sacrifice which is useful in PvP and PvE (mostly on the tank). 30% damage mitigation for 12 seconds for any target you choose is great utility, and its only on a 30 second cooldown (your pet absorbs the damage).
In PvP Scorpids have been popular in drain team setups, as a Paladin has more trouble removing Viper if you have other poisons up. Drain teams are not quite a part of the game yet, since burst is so powerful at the moment. Since Scorpids no longer stack their poision, they are no longer popular for drain team setups.
My problem with a Scorpid in PvP is that it is a bit too fragile without Heart of the Phoenix and Lick Your Wounds. I believe a Tenacity pet will only get better once pets are not so easily killed, but as of right now, if you find your Tenacity pet dieing too quickly I would just switch over to Ferocity at the moment.