topspeed,

It's possible that dimples would help reduce drag for that shape, but it depends on several things. If the flow tends to separate early, say around the top edge of the backlight, then forcing the flow to transition to turbulence before that point could delay the separation, thus reducing drag. However, if the flow is already turbulent by that point, then adding dimples probably wouldn't have any effect. It's also worth noting that there's nothing special about dimples; other kinds of surface features can be used to generate turbulence. For example, a fairly small ridge at the top of the windshield, which might exist anyway, could be an effective turbulator.

If the boundary layer naturally stays laminar and attached all the way back to the sharp rear edge (unlikely, I would guess), then no kind of turbulator would help. There's no way that the boundary layer would stay attached past that point, turbulent or not, so inducing turbulence in that case wouldn't reduce drag at all.

banktoturn