After again posing the question to Suburban I got a response from their senior product engineer as follows;
The two metals only have to be electrically connected, not physically connected to one another. The connection can come thru the electrolyte. I’ve attached some light reading on the subject from Materials Science and Engineering: An Introduction 5th Ed.
So I will leave it at that. Functionally for the RV water heater it is a moot point as I have always used tape on the threads and upon removing the rod there has never been more than strings of tape left after the threads cut, shredded, and compressed the tape into the voids to seal the threads leaving most of the threads exposed to metal to metal contact. And the rods have always corroded as designed and never leaked.
