In my experience, character levels grant hit dice, unless you are taking monster classes, which miss hit dice because they are accounting for level adjustments. So the official rule is just (hit dice)+(level adjustment)=(character level for experience purposes). Now a problem arises when monster hit dice are being treated like class levels when, in fact, they are sad and lame. For an example, lets take the
bugbear:
Bugbears As Characters
Bugbear characters possess the following racial traits.
+4 Strength, +2 Dexterity, +2 Constitution, -2 Charisma.
Medium size.
A bugbear’s base land speed is 30 feet.
Racial Hit Dice: A bugbear begins with three levels of humanoid, which provide 3d8 Hit Dice, a base attack bonus of +2, and base saving throw bonuses of Fort +1, Ref +3, and Will +1.
Racial Skills: A bugbear’s humanoid levels give it skill points equal to 6 × (2 + Int modifier). Its class skills are Climb, Hide, Listen, Move Silently, Search, and Spot.
Racial Feats: A bugbear’s humanoid levels give it two feats.
+3 natural armor bonus.
+4 racial bonus on Move Silently checks.
Special Qualities: Darkvision 60 ft., scent.
Automatic Languages: Common, Goblin. Bonus Languages: Draconic, Elven, Giant, Gnoll, Orc.
Favored Class: Rogue.
Level adjustment +1.
using point buy: 16+6+6+4+0+0, wielding longsword, heavy shield, chain shirt.
HP/AC/att/dam/Fsave/Rsave/Wsave
If there are no hit dice:
bugbear1/fighter1:
13/22/8/1d8+6/7/3/-1
Horc0/fighter2:
19/19(dodge)/8/1d8+5/7/2/-1
bug1/fighter3
30/23/10/1d8+6/8/6/0
Horc0/F4
34/19/10/1d8+7/8/5/0
With HD:
bug4:(morningstar)
26/23/9/1d8+6/4/6/0
Horc0/F4
34/19/10/1d8+7/8/5/0
The extra constitution means that hit points will eventually catch and then exceed the plain-raced counterpart while AC is consistently higher. Damage is generally superior, although weapon spec can compete if not using two-handed weapons. Without the spare feats the saves have dropped off but not to a massive extent. Basically, leaving hit dice out is just too much of an advantage, while putting them in is too weak, maybe half them and round down? It would be consistent with single hit-die races...