Is there anything special about the Moldering Ursine that makes it a good PvM combat pet?
Is it comparable to a Hiryu tank?
Or should I use those 200 points on something else?
I think the main allure is it's a mountable life leech pet. Also, the stats when you claim it are always the same at its base, so no worrying about RNG.
Yes. The Moldering Ursine definitely has it's uses, and can be particularly effective as 120 Chiv+AI, especially for a Disco/Tamer. Their self healing capability scales with their damage output due to Life Leech, so they can out heal Tritons/Cus when dishing out high damage.
They're also able to take full advantage of "Combat Training: Berserk" due to Life Leech being the only thing unaffected by Berserk's healing debuff (for pets at least). I've seen 430+ damage EoO+AIs from berserk Moldering Ursines and Ossein Rams.