Stewing meat with vinegar or adding it after Wild turkey legs are rather tough, and some hunters even throw them away, but I decided to give it a shot in a slow cooker set at the lowest setting for 8 hours, with vegetables. I definitely like vinegar or citrus in my stews but as a condiment before eating. I was wondering whether adding it before or while stewing might be a good idea, such as helping tenderize a questionable piece of meat as is the case here. 

At the same time, it's a rare cut of meat so I would rather not experiment too much: Is long stewing tough-ish meats with vinegar a good idea or should I add it after stewing or before eating?
Probably the turkey legs are frozen right now.  Why don't you experiment on some turkey legs from the store?

Probably acid would be good to help break down tough cuts.  I have not heard of stewing in vinegar but definitely stewing in wine.  I stew in V8 juice pretty often.  If vinegar is what you dig, try stewing some regular turkey legs, with an onion, cinnamon stick + star anise and some navy beans to soak up flavor.  I would pick apple cider vinegar for turkey if you had to use vinegar.  If I were doing it I would use apple cider +/- cheap white wine and save vinegar for a condiment.  Or I have heard of these things "recipes" you might find.

If you like what you make with the farm turkey, then you can try it with your wild turkey. If you screw up farm turkey it will still be edible and you can tweak it for round 2, and round 3, until you get it right.