If there is only one SA AOC holder involved then it should not present a problem. Aircraft on their AOC Ops Specs. Crew employed by same AOC, maintenance questions etc.
Its all about operational control, who is running the show when it comes to a wet/damp lease between 2 SA AOC holders.
The law provides for the SA AOC holder with the aircraft on their AOC to retain operational control.
Read Part 48 (?) new regs dealing with leases. The problem is the CATS are not published yet and it is open to interpretations.
As already suggested, in fact the law requires that ALL lease agreements must be approved, thus go to CAA but make sure you know all the answers when it comes to "who controls the operation"