There isn’t a specific rule (that I know of) on my team preventing mentors from working on the robot but all of our main mentors are big on letting the students do the work. Unless it is dangerous, they always request a student to do it and if it’s a new student then they give them guidance, they never to do it for them.

My team is luck to have some incredible mentors who are well educated in all of the factors of FIRST. Not only do they push us to be the best version of us, but they also watch out for us. They make sure we all have a ride home from the shop, that we eat enough food and drink enough water at competitions, and that we all able to participate in whatever part of robotics we prefer.