Considering that in most cases you'll be plugging in your CAN bus only once when you wire your robot, I don't see a concern with the RJ series connectors. Your land line telephones are also connected with RJ series connectors and they also take a fair amount of abuse, their connections have a fairly low failure rate in that environment as well as in network systems.
As a model railroader, we use a similar connection for our data bus standards for digital command control with very few problems. It should work well.
All I can say to FIRST is... "When
CAN we play?"
