Can a collegiate VexAI team also register as a VexU team to compete in both competitions? This would seem to violate <R1> section d, since it states that a robot may not compete under multiple team numbers. But the spirit of the rule seems to be to prevent multiple teams/organizations from sharing a robot, not to prevent one team from competing in both VexU and VexAI.
Using VexAI Robots in the VexU Competition
Yes, the same group of Students may register as both a VEX U Team and a collegiate VAIC Team. Yes, they may use the same Robot for each competition (provided that no other Robot rules are violated in either one).
R1 is intended to apply to Teams within the same REC Foundation competition platform / grade level. In a tournament, a VEX U Team and a VAIC Team would never share the same field, Skills ranking, Alliance selection, etc. (of course, the Robot cannot be used in multiple programs by separate groups of Students, since that Robot would not represent the skill level of both Team(s), i.e. would be in violation of rule G6)