A passive radiator is like a duct in BR. The mass of air in the duct might be compared to the mass of the passive diaphgram. If you make a hole in the box while using a pr you add a big air leakage so the system is unbalanced >>not working !
The PR can not work properly since it requires that the air in the enclosure be "stiff" so that it can move. There will be some movement of the PR though.
I suppose at frequencies where the port is working, IF the PR is tuned to the same frequency, there may be some sharing of the energy... would be an interesting experiment, but in the case where they are not tuned to the same frequency I seem to think that the PR will not do much...
Sure... very different than trying to run both a port and a PR from the same volume in "parallel".
One could substitute a PR for all or some of the ports.
Since the PR tends to act more like a closed box at freqs above and below its resonance, there may be some benefits to choosing the location WRT this function.