The old ones have the same dps, they just have half the hp. You can tame those and they won't be deleted.
I'm not sure how much you want of the nuts and bolts here, but in spite of the fact that they look like the old hell hounds, the game sees them as an entirely different monster.
And yes, the ones in your stable will delete themselves too.
I do want to put out a new improved hellhound, and I intend to make it tamable, but it won't be this one.