Hmm, 9 HDs seems rather low. It has more Str and to-hit bonus than the proverbial raging 9th-level Water orc Barbarian. Like, with base 18 and a +2 item for both, 48 v Str vs 28 Str and +21 vs +18, bonus damage +19 vs +13. Accounting for PA for a natural weapon for the hound and a 2-handed weapon for the barbarian at -7 penalty for the hound and -5 for the orc (so +14 in the end for both), that's +26 vs +23, and then secondary natural attacks for the hound. But also wayyy more HPs and resistances of all kinds, is pretty much immune to grappling, etc. etc. Sunlight vulnerability can be accounted for without too much trouble. Body shape is a pain, I agree.

If we put it at, say, 13 RHD, then the barbarian gets Greater Rage and that ends up at hound: +23 vs barbarian: +23. That seems a better base to me. How about that?