Can V5 teams use old broken cortex motors as weights
no since they only reason they would be on your robot is non functional decor
and they are being used as weight so then they are functional. If your robot is tippy look for anti tip suggestions. Weighting down a bot is an inefficient solution because it will add strain to your motors.
Screws, axles, plates, all work as good counterweight solutions, do not know why you would want old motors as weights
^ Teams may not use old Cortex parts as non-functional decorations