To answer your question directly, I will say it is not considered cheating. While I doubt people will get mad at you, some will think it a little unfair if both of your robots end up in the finals together (Same team or opposing teams).

I don't know about ethics, but if I were in your situation, I'd get to work on getting more sponsors so you have the materials to make 2 different robots. I know more people get the "driving" experience, but at the same time the rest of the team will only get half the experience.

It's like 2 teams designing 1 robot. Each person only gets half the work of the normal person, since there are 2 teams. Plus, it wouldn't be as fun!

I say if you can, get the money to get the extra resources to build two different robots. It's totally worth it in the end. In that scenario, the two teams act like two teams the whole build season, and it'll be even more fun to go against each other in matches to see which robot is better!

If you really want to share something in design with the other team, do what 254/1868 do, share a similar if not exact same drive train/base

Hope this helped! And remember, have fun with it!