Do these rules apply only to Exchange or do they also carry over to Communicator? Would I need to do something with HOOPS exchange in order to get PMI data in the web viewer?
in general the page you referenced also applies to HOOPS Communicator with regard to the supported formats for PMI. HOOPS Exchange is used under the hood in HOOPS Communicator so there is nothing to do on your end to get PMI into the viewer.
There is a setting in HOOPS Converter that controls if PMI is imported (–import_pmi) which should be set to true by default.