Air Tabs work much like an open air NACA submerged duct inlet. They influence and mix (till if you will) the boundary layer by drawing faster high energy air toward the surface.
Sure there are the counter-rotating vortices but these are a byproduct of function. The vortex filaments are not what delay downstream flow separation but rather the higher energy lower static pressure flow pushed against the surface making it stick longer before the boundary layer pressure gradient grows adverse. This is useful in extending Coanda flow attachment. That said aft facing Coanda attachment surface suction is generally bad for overall vehicle drag unless that pressure investment can be profitably applied saving a greater drag downstream, as a fairing costs drag but saves a greater drag as its return on investment.
