Probably correct, I expect Mr. Christen knows a thing or two about such subjects.
My own view is that I'm not quite ready to start drilling holes in my shiny new CF RC yet, and glue is a very messy one-shot affair
So, the top dovetail which seems pretty rigidly attached to the OTA, is the next best thing, using good ADM attachments and rings, especially when it's just holding a very lightweight finder and camera. Probably more chance of micro-movement in those little rings than in the rigidly-attached ADM D plate on the bottom of the OTA, so the whole OTA+mount should be OK.
If it was a finderguider on a cheap set of rings attached to some cheap OTA rings, then yes, I'd say that would have lots of potential for movement, but the GSO RC8 ringless setup, especially with a lightweight CF OTA, really has a very strong overall structure and the finder guider works well, especially as there's also no internal OTA mirror movement to worry about.
In this scenario, in my opinion the PHD and EQMOD settings are the most critical items in getting round stars. YMMV of course.