I'm new to 35mm adapters. I just used a Redrock on a recent video shoot and really liked the look. We used a 14mm Canon, so the image was incredible.
I currently own a Panny HPX500, which means 2/3" chips and lens. Do 35mm adapters on, say, a 1/3" camera make that much more of a difference over my setup? Will I notice a dramatic difference in DOF compared to my 2/3" rig?
I like the idea of using prime lenses. I'm considering adding a 35mm rig to my equipment if I can have that much more control over the image.

I would say: yes, because 2/3" is still not big enough to make a real difference in Depth of Field. I think starting from 4/3" to APS-C you really have the depth of field to compete with a 35mm adapter.
Only I don't understand "We used a 14mm Canon, so the image was incredible."
Do you mean an f1.4 lens. Because a 14mm wide angle lens doesn't give you much DOF, so I wouldn't bother using a 35mm adapter in that case.

Sorry, I did mean the 14mm lens. i know there was no dof effect, but I just liked the image we had, and the fact that we could change out to any 35mm lens we had available.
That's a pretty new concept to those of us who normally work with 2/3" zoom lenses.

Glen, what you've said right here is what filmmakers said back in the 50s - except that they said it the other way around.