Even back in those days, with limited media, I doubt that they could or would carry off such an elaborate ruse. Based on todays brother combos in GCA, I suspect the brothers might be out there trying to prove they were equals, not support the other. For that matter, look at any prodigy, such as our Presidents, and name one whos brother sat on the sidelines (without good reason.) Think Billy Carter and Roger Clinton. The Bushes seem to be a little more consistent in their abilities, (whatever those may be!)
Secondly, Brad has documented that DR made the train trips, etc. Had he known absolutely nothing about design, I am sure some sharp client would have noticed somewhere along the line.
I suspect DR helped his brother greatly, but could be wrong. It would be interesting to know.