oak painted black > how to refinish

I'm not sure what your definition of refinishing is but, yes, if it is solid oak I can't think of a reason why it couldn't be refinished. From the question I'd have to assume you can but I can't see what it would be.

Leave it alone. I recently refinished the stairs in my house. They had been stained a very dark brown(thank you 70's). I found that the oak held the dark color deep in the grain lines. To remove the color totally I had to sand the hell out of the treads as well as bleach them. The result was still poor. If it was a solid piece and it would look good in paint I might consider it.

I intentionally painted some oak gloss black with simple "Krylon-esque" spray paint. "Grain" is visible. Think it would be a bugger to remove. Suspect I'd have to take a 1/16" - 1/8" or more of wood off to get it all out.

Are all sides painted?

Pete