I'm not entirely sure what's up with bebiliths. They're supposed to hunt other demons, yet their racial features fail to help them do so (poison won't work, no MM demons wear armor, and tracking or webs are useless if your foes can teleport). They're demons, but don't belong to any of the major demonic races (tanar'ri, obyrith, loumara), which is weird in itself. At least their lack of SLA's makes them easier to adjust for player use...
Bebiliths have 12 outsider RHD, as well as the chaotic and evil subtypes. They are reasonably quick for a Huge creature and can climb if necessary, but lack in movement options compared to other demons. Ability scores are pretty good, with high strength and constitution and above-average or average other abilities.
Bebiliths have few special attacks compared to the plethora of summons and spell-likes other demons get. They can rend armor if both claw attacks hit. With the amount of monsters wearing actual armor getting smaller and smaller as one levels, I doubt it'll come up often, though. Bebiliths also have constitution-damaging poison, but with poison immunity being so easily available I recommend defaulting to a mouthpick weapon and only using the poison when necessary.
Then there's web-throwing, which is basically an improved version of a net. With entangling being a so-so buff (unless paired with other dexterity penalties) and the fact that you're limited to four webs a day, I'd use my actions in other ways.
Finally, there's at-will self-only supernatural plane shifting. With wizards gaining plane shift in a single level and clerics already able to access it (with both these classes able to use it offensively or take others along), I doubt it'll be useful except as a panic button, or perhaps to function a the party's interdimensional shopping cart.
The bebilith may raise interesting logistical questions, but it's not a strong monster by any means. No LA is necessary to balance it.