Actually, this is incorrect.
For physicians, SOME fellowships are approved. However, most internal medicine fellowships (i.e. infectious diseases, cardiology, GI, nephrology) are NOT approved. You must complete your service obligation PRIOR to doing your fellowship.
The only fellowships approved for IM would be geriatrics or addiction medicine. If you're planning on specializing, then I do not recommend applying for this scholarship.
Most of the NHSC sites, in real life, are not in prisons, no worries. :-D