Occlusion shadowing as self-shadowing (if it can be used that way) would work nicely for something like an Orion, but there'll be troubles with ships like the Hecate or Ravana.
Light occlusion is shadowing, you guys should be more clear about what you talk about. (ambient occlusion is shadow for a light which comes from every direction.)
If you mean with occlusion a method which produces a inperfect shadowing in terms of accuracy and hope that it doesn't look too offending, there are several although non proved ways.
Most of them have problems in terms of asset generation and/or rendering.
Something like low-res volumetric distance field for each ship could do the trick.
Basically one would trace against it and see if the light is behind something solid, as it is distance field one would have acceleration structure and ability to change the blurriness as well.
It would not be accurate, but it would give general sense of shape.
Shadows from other ships could be done as drop down shadows, but as always with combination of different methods a shadow mask buffer is a must for this. (render shadows to buffer and then use it to occlude the light.)
Here's couple of links to distance fields.
http://hyperfun.org/FHF_Log/Bastos_GPU_ADF_SMI08.pdf (idea of using distance fields for an object representation, we do not need nearly as high resolution.)
http://www.valvesoftware.com/publications/2007/SIGGRAPH2007_AlphaTestedMagnification.pdf (valves distance field text rendering.)
