This is not correct. I have had Fortress and Prismatic Ray (RCA and bus sync revs) synced to multiple other timings. They are both only looking for timing pulses and have no concept of timing format.
I haven’t thoroughly tested Navigator in HD timings but the sync input is actually not 100% necessary for it to work just fine in HD. The rear sync input is there to correct interframe blips that might happen at certain speeds with the internal quadrature oscillator. You don’t have to connect a sync cable to it at all to use its functions.
The only Expedition modules I’m aware of that simply will not work with timings other than NTSC/PAL are Visual Cortex and Liquid TV. The only Orion modules I’ve tried that do not work with timings other than NTSC/PAL are Memory Palace and Diver. I haven’t tried Escher Sketch with HD timings but that likely would be a similar issue in correcting interframe blips on its output like Navigator.