I totally agree with Ralph on this one. Rommel and Von Arnim didn't get along very well together, so I see no reason why Rommel would give him a pistol.
Your friend definately needs to get much more facts before making any claims to this piece.
Rommel was highly photographed during his tour of the "Atlantic Wall". Looking at the photos, it appears Rommel is wearing a small SLP in a softshell holster. Possible a Walther PP or PPk, or maybe a Sauer 38H?
I don't recal seeing any photos of Von Arnim wearing a pistol at all? Perhaps one of our members here has one?