On the whole has far has I know not many Union soldiers served in CSA irregular units. The only example that I know of was a Lt with Col Mosby and I seem to recal there was a former Union soldier (mentioned by Leslie) who served with Quantrell. Interestingly enough while more then a few conventional CSA soldiers defected to the Union Army during the CW I am not aware of CSA irregulars defecting to say Union USV Calvery units. i could be wrong about the latter it would be interesting if that occurred.

Thanks;
Leonard