The difference between rec and open gym is coaching. Open gym is usually just show up and use the equipment on your own with coaches just supervising (and they usually have their hands full doing that!). Rec is where you are actually being coached in an organized fashion, but it is usually more emphesis on gaining skills and having fun then perfecting skills for competition.
At my gym there are certain things that only gymnasts can do, like use the high equipment for example. But it is up to the coaches who is a gymnast and who isnt. So like when I was dating a gymnast and she would "coach" me, I was allowed to do stuff that only gymnasts can do because I was being spotted and my gf actually worked there as a coach. Your best bet, ask the coaches!