Could the sea waves interact with the ships and hover crafts by wallowing (ride on waves) them ?

are there actual waves in spring, as opposed to just graphics?

No. Reason: Non, deterministic physics leave many players with a feeling for having been cheated when it came to succes.
You dont built 3 berthas and then watch in awe as every shot they fire always crashes into the huge waves, just because somebody micros that too good.
Theres a thin Line with ingame physix, and this line is were the new Battlefield "CC:Generals" might run into troubles.

Ships wobbling in water can be faked, like eg zeroK does it.
I know that because it gets spammed in lobby chat all the time.

BA has wobbly ships too.

Can you get them to tip over entirely?

Absolutely, by making them run into each other. The engine takes care of the rest. You can even go redneck epoch tipping with super engine bounce :D

cool :D

I had some thoughts of making a tsunami effect, but it would be really tough to do. At least if it has to gather a lot of debris.