NOAA can clear a diver to dive off their boats, as a 'guest' or 'visitor' or something.
I've had this clearance, whatever it's called. There's a limit to the number of times you can do it within a year, a dozen or so.
To qualify, you have to submit a copy of your c-card, and a "diving resume." Maybe I had to do that in lieu of a logbook (mine disappeared many years ago and I meant to start a new one but never did, and since most of the operations I dive with already know me...)
And, most bothersome, you have to submit a physicians' form (supplied by NOAA) vouching that you probably won't stroke out on their boat.
And you have to give them a new physical form every year. Now as a middle-aged guy I try to keep up with my physicals, but yiminy. I don't have the clearance currently because of this.
I'm sure there are other limits on what dives and activity that you, as a non-NOAA diver, can do off their boats, like no "working diver" activity. But I've been to 100 feet with them, and taken pictures, so I was happy.
I know a Keys dive-shop owner and sanctuary volunteer who got tired of the annual guest-diver renewal so she checked into seeing what it would take to become NOAA certified. Her conclusion: Forget about that; it's insane!