anyone running an alternator off their 3rd member?

drag would be equal, regardless of a location, pending pulley diameter. Low speed charging would be low, and no charging would occur if the car is not rolling(obviously). I don't see any advantage to mounting it like that. If you had the battery in the trunk, it would simplify the wiring a little, but other than that, I'd say its pointless.
 
the reason it is done, or was done, on race cars is to move weight to the back of the car. for the street it really doesnt matter, but at the track every little bit helps.