Any visable differences or can one pass for the other?

There are detail parts differences and key identifying features - mostly the wheel covers (access hatch shape), maybe type of radiator, grab handles near the tail...

Your D.Va kit will come with parts to build either / or - just download the manual from WnW website for the version you want to build. You can even build a D.V out of D.Va OAW with exception of PE parts...

Now, it's not out of realm of possibility that OAW parts would find themselves onto Johannisthal built aircraft - very true for late War aircraft, like Fokker D.VII and may be true for D.Va... In case of D.VII, OAW parts were specifically sought out by ground personnel, so spotting identifying feature would not identify aircraft's original manufacturer...

In the end - tell a story

Thanks Ivan. Been a while since I was paying attention to the WNW kits so the D.v and D.V a are booth sold out and only one available is the OAW version but if I can build a D.V out of that it works for me.