VAA have leased the Air Atlanta aircraft simply because they do not have the aircraft to meet the demand. I don't think the pax would be too happy if VS were to canx services due lack of acft. Leasing other acft is common practice with many airlines. As far as I am aware they are JAA ops approved, and TF-ABA is a fine ship. Air Atlanta provides the flight deck (who gives a flying **** what nationality they are) and VS use their own cabin crew along with Air Atlanta using an IFS (I think??)
This operation is only temporary and upon further delivery of their new -400's, the lease with Air Atlanta should soon be phased out.