I suppose you could mount a rod piezo underneath a hard tail bridge, and it would probably work, but it would not be the ideal way to mount it. A rod is intended to be sandwiched between a saddle and a bridge, so the strings press on the saddle, and the saddle presses on the rod. You could cut a small slot for the rod to lie in, with part of it sticking up, and then mount the plate of the hard tail bridge over it so that it compresses the rod. No clue how well that would work, and I would not personally be inclined to try it.
A rod also has the "indentations" where the wafer pieces sit, so you can get each string to transmit their sounds independently of the other strings, which is what a disc piezo can't do.
My recommendation is to use a magnetic pickup in combination with the hard tail bridge.