Cicopo-
No, I'm not implying that they place a relatively new diver with a group of highly experienced divers, and allow the new diver to dive with their tank. I was replying to your comment that Sand Dollar has "timed dives or even worse when the first diver is low on air everyone surfaces, no matter how much air they still have."
I have never found that to be the case with Sand Dollar. We've always had great service, great dive guides, and have never been required to surface when the first diver is low on air.
In fact, everytime we've been there, I've watched them check the levels of divers in advance, and do their best to place, accordingly. We ask them to place us with other experienced divers. They do their best to make that happen.