Hi @yeclek,
There’s some discussion here about underwater wifi - the range is apparently about 5-10cm, and you likely need an acrylic enclosure. At a guess I imagine Bluetooth would be similar given it’s a very similar frequency band, but I’m also unsure whether it has the same kind of broadcast strength (so it may not be as effective).
From what I recall there are also a few different posts on wired connections to control GoPros. This one might be relevant, and it may also be worth searching the forum for some others 