I wouldn't trade K-Rod for Napoli, given your team/scoring. Since OBP is not a stat, Olivo has decent enough value (his SLG brings his OPS up just enough to off-set the fact that he can't draw a walk).
Ramon Hernandez would be a better option than Olivoi IF he played every day. As is, I'd ride Olivo and hope he heats up down the stretch. He's a streaky power hitter, and could have a 4 or 5 homer week or two in him.