Not sure how well the swim. Hooves are quite different than flippers.
I suppose they could use the weight of their giant sized weapons to keep them on the bottom of the sea so they could battle down there.
However, those same weapons are so big and massive that there would be a lot of resistance to the weapons.
I do think it’s a good question as to whether their wings are nimble enough that the could be used to propel them through the water. Some birds can do this. But these aren’t arm wings, but back wings.
On the other end of the not breathing scale, if they had rocket packs, fighting in space would not be too much of a problem. It’s just moving.
Schwarzenfurze would be fine of course, wouldn’t even need the lighter (which wouldn’t work in a vaccum) simply releasing gas would propel her forward.