Who's an Evil boy? You are! I regret nothing!
Hell hounds have 4 outsider RHD, with the evil, lawful, and fire subtypes. Their ability scores are pretty bad, evening out to a net -2. Natural armor and speed are decent, but not remarkable.
Hell hounds also have a breath weapon that's pretty underwhelming, and get to add 1d6 fire damage to their bite attacks. Greatswords are still better.
Finally, there's a reasonable bonus to hide and move silently. They're not the worst skills on your list, so go ahead and put some points in them.
All around, hell hounds are simply underwhelming. Whereas other monstrous races tend to have at least one thing they can perform well at, here it seems you're forced to pick between bad blasting or bad melee. Even as an entry for Fiend of X there exist better options. -0 LA.
I invite you to think of any time where adding more HD to a monster and adding a single die of damage to its special qualities increased its LA. -0 LA.