This may surprise you, but I actually quite like inevitables. I know, who'd have guessed?
Kolyaruts are the middle child of the three kinds presented in the MM, with 13 HD. It's unfortunately Construct rather than Outsider type. They have okay stats, though their medium-ness and low strength make for a less potent melee combatant than one might wish.
Better are the special abilities: semi-relevant SR, fast healing, DR and construct immunities. The Enervation ray is not that interesting, but the Vampiric Touch (note that it should deal 6d6) is, as it apparently gets iteratives. I did some math, and something as simple as a Kolyarut 13/SA Fighter 7 can easily deal 200+ damage a turn (healing the same amount itself), as long as its target doesn't have exceptional touch AC.
Finally, the SLAs. They're a smattering of low-level spells, but the fact that they are at-will make some of them decent (Invisibility for every party member! Discern Lies on every NPC!). Besides, it's not like a kolyarut will have to depend on them in combat.
I think a LA of +0 is good here. Kolyaruts can make a fine if unconventional ingredient for melee characters, but their potential need not be limited with a higher LA.