So Roger Stone has a tattoo of Nixon's face on his back. Will this help him or hurt him in prison?

The only thing worse would be a picture of Nixon’s backside tattooed on his face.

Depends what Roger Stone is in to; there might be oldtimers there that always have had the hots for Slick Rick.
And act on it (and stare him in the eyes).

What would possess a person to have Nixon tattooed on his back? What sort of a lucking foonatic does that?

Brings to mind the old saying “Dick Nixon before he dicks you!”.

He’s not going to the sort of prison in which you or I might find ourselves.