I hove both in my tank. The puffer has been in for about a month, and the shrimp has only been in there for a few days. The puffer has "looked" at him, but yet to peck. The shrimp does spend a lot of time in the back of the tank behind a rock, but not in a necessarily "secure" spot.
He also leaves my two mexican turbos alone.
I have heard it is hit or miss with the valentinis. Some have had success, while other have had an expensive "snack" for their puffers.