This has been discussed before, but the defining characteristic of a rep is a watch that uses a patented mechanism or trademarked name/logo without permission.
The fact is there is nothing about the look of UBOAT watches that can be trademarked beyond the name.
Believe me, if you could trademark a general look, or appearance, Rolex would have done it long, LONG ago.
Panerai gets away with it by the simple fact that the trademarked the image of the shape of the crown guard. That's the legal basis they used to force RXW to stop making/selling the MM20. It's also why they can't stop RXW and others from selling Radiomir or 6154 style "homage" watches - they lack the CG shape, so there is nothing they can do legally.