I have researched this a ton.
There are three types. Supplied, SNUBA, and hookah.
Supplied is the professional way. Like fresh air for SCBA.
SNUBA is a trademark, but i take it to mean a tank(s) that float above you.
hookah is a compressor that is above the water line.
Advantage is that you have air that is only limited by your source.
Since you are already on one hose, it is easy to add a wire or two to send communications and potentially video topside to your safety people.
Disadvantage is that you can only go as far as your tether. Also, if you are using a raft style, and it is unmonitored, it gets flipped by wake or wave, or the raft is poked...
Wash is tangling hazard. If the environment is going to snag, it can get the hoses on your scuba setup just like the tether/umbilical.
I know that you know what you are doing is exceptionally hazardous as-is. And you know that submerging to clear garbage is some of the most dangerous marine/shore operations you can do, so I won't beat you up over that, except to say to do it the way they would want here you'd need multiple, multiple certs. (Open water won't even begin cut it, to pardon the pun). That would be borderline commercial hardhat work. (Read about people dying just cleaning silt out of drainage pipes with a vacuum, for instance)
The real question would be, what does your organizations' insurance cover? Would it be a workmans' comp issue when you get injured doing this?
Far as rendering an opinion on the units you mentioned, none are designed for strenuous exertion, which is a real issue with underwater operations. Neither are for commercial operation, but borderline pool noodling and having fun in clear water. You outbreathing their capacity trying to yank stuck stuff out of the muck is a clear possibility.
You would still need some sort of rescue (what sport divers call a bailout) bottle setup in case you are entangled and lose your tether. Or have to cut your tether away.
Is there a local salvage company that can sherpa you guys a little?
Thanks for helping your local environment. Don't get deaded doing it though! The surface may only be three inches away, but if you can't get there before you run out of air...