This is my second goal for autonomous. Yes it is legal and possible. Your robots do not need to start in their respective lanes, so potentially you could have two robots right next to each other. Also the ubertube must only be in contact with your partner so after capping your you could go back and grab it. I think its possible to achieve it with a compass, gyro and rangefinder, and be fairly accurate. If you want better than about 25% with the second cap you will have to use the camera.
Our autonomous robots typically use a mixture of "blind movements" (no sensors)" dead reckoning"(anything but the camera) and the camera. If you have the camera you can do blind movements. if not stick to using feedback from the sensors. If you want any more info just ask
