Can i use a propane grill or do they restrict to only using the fire pit and grill?

Yes. No restrictions

Instead of their fire pit I use an old washmachine drum. Never had any problems with the park rangers. It works so much better.

You can use a propane grill

Definitely.

We used a propane grill every night the last time camping there.

Propane grills are allowed.

Yes. I take a propane grill every time we go. Not a problem