NOT!

Hydro-lock is still hydro-lock... If the air intake is below water, it's still a big problem.

Submerging the engine itself isn't something that's fundamental to gas or diesel. If the engine block can take the thermal shock, then it's OK. As long as there aren't any other ways for water to screw something up. Like breather vents for the transmission, electrical connections that short out, water getting on your clutch, or a zillion other things that you don't usually think about.