You could try using a dynamic paint modifier that makes a vertex group to emit particles from when colliding with the ocean.

Here is a blend file with an example setup.

 (Note, only worked for me with the 2.68RC)

However, there seems to be a bug where the particles keep emitting from the same spot..

You could try using a dynamic paint modifier in weight paint mode that makes a vertex group around the object colliding with the ocean, which you could use as an emission vertex group for some particle systems.

Here is a blend file with an example setup.  (Note, only worked for me with the 2.68RC)

However there seems to be a bug where the particles keep emitting from the same spot.

This is a limitation of the particle system implementation unfortunately. http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Particles

The location of emitted particles are determined in advance now and stay fixed, so this can't be animated. There's been some working on designing an improved particle system that can handle such animations but it's not finished: http://code.blender.org/index.php/2011/03/paged-buffers-for-particles/