Since they only eat ectoplasm, and are intelligent, one can assume they are harmless to Gate-ers.

I can see this going in a non-comedy campaign, and I can also see it going in a comedy one. Depends which aspects you play up.

And as for the Silver Teeth, this creature can't defend itself against people who are truly on the Astral plane. Well, it can, but it loses a ton of efectiveness. Kind of like fighting a fire elemental in the middle of the ocean.