I may well be wrong, but I was under the impression that monsters were not divided into roles as such, rather that monsters would be represented as kind of templates which could be layered over the basic framework provided by the role.
As such, you could have a Balor Brute, a Balor Skirmisher and so on. Depending on what role you wanted it to take in the fight. This might explain the lack of the disguise self and so on SLAs in the spined devil writeup - the "Skirmisher" version doesn't get them (because it doesn't need them to skirmish) but the "Infiltrator" (or whatever) version might.