Generally I'd say Monster Girls are kinda borderline. You CAN get away with it in /e/ or /h/ but it depends on what we're specifically looking at here.
No one wants to see a chick with a bunch of tentacles, or in "most cases" a freaky spider chick; but half snake. or a mermaid, harpy, or something like what I'm posting...you can probably get away with.
Slimes would be a 50/50.
In short, you can, but do so at your own discretion.
