Correct, except you don't have to have park hopped to try for RotR, you just have to have entered your starting park (I think this is what you were asking, but wanted to be clear), but you do have to have a park hopper ticket.
When trying for a boarding group for the opposite park you're starting in, it can work a few different ways.
1. If you get a boarding group at 7 in your starting park and ride before noon, you can get a boarding group at noon in the opposite park.
2. If you get a boarding group at 7 and don't ride before noon and would rather try for the ride in the other park, you can cancel your boarding group before noon.
3. If you don't get a boarding group at 7am, you can try for a boarding group in either park, but not both.