Speaking of Carcass Crawler, would classes from the zine be permissible, or would you prefer to limit material to what you personally have access to? It's official material made by the same people who designed the game. I only ask because a copy of the first issue fell into my lap recently.
*EDIT* There I go talking about reading the Big 16 and I forget the wording of point 16.
I'm very new to OSE as well, but have been reading up on it since a friend might be running that megadungeon Arden Vul with it sometime.
That's the impression I got from reading the Big 16. Classes and race-as-classes are on the table, just no demihumans taking "normal" classes.