Yes, yes it is.
For one thing, as awesome as welding is you are usually going to have two problems:
1) Frame distortion- Every frame I have designed that has been welded has warped to some degree (especially aluminium), this is not a happy thing to deal with (wheel contact, conveyor alignment... ).
2) Skill- My team was lucky to have a veteran welder around, but I have seen what happens when a new student tries to weld aluminium. It becomes more like modern art, and less like robot frame

.
Bolts lose in the weight and remaining tight categories.
Rivets are light, easily installed and uninstalled, and create pretty solid joints when done correctly. I think every FRC robot has at least one application where rivets would be the most useful of all fasteners.