A symmetrical rear wing profile will work just dandy
Especially when a bit experienced, as then you dont want it to pull down much anymore, as this will give the kanguroo effect instead of a balanced foil that dont go up nor down at changing speed.
I have got several symmetrical rear wings over the years, works just fine
One could say, that in theory if you always have a little bit of downward lift, a slightly negative camber profile would be lower drag and max adjustment window (meaning you can push forward or rearwards without stalling the wing), but I honestly think the difference is not really noticeable
Especially because, in tight carves the rear wing will actually lift up and not down as you stomp harder down with your rear foot in tight carves - so here you dont need or want a negative camber.
Might be wrong - just my view and somewhat experiences.
PF