I think the small upside (a single 5-star rating contributes very little to app ranking) is outweighed by the potential downsides (it can be a turnoff if the user sees that because it strikes of astroturfing, which seems a hot topic these days; it violates app store guidelines, though there's a close to zero chance of that being enforced).

To me it seems like unnecessary risk for little benefit.

Edit: And product reviews are not the same as voting. :)