Personally I would expect some sort of check valve in the system for drum brakes. Disc brakes, no.
The Ford master cylinders have a removeable rubber check valve installed in them for the rear brakes. The discs you want to fully retract so you don't normally use a check valve with them.
I don't know Wilwoods. Perhaps they have a different design in the calipers?
It is just something I would not expect to see in a disc brake set up.