That territory is considered full-friendly after you captured it during your turn.
So now that its after your turn, its defiantly friendly to the point where you can land planes there.
tl:dr Yes
I think you meant to say “definitely”
Here’s the situation. The US lauches a successful attack on sz6 and invades Korea. The next turn Japan counter attacks sz6 and clears it of US boats, but Japan also loses all the attacking forces, so the transport survives. Japan then places 2 destryers in sz6. Can the transport load the troops from korea and move to Okinawa and launch an amphibious assualt there, or is the sz6 now considered hostile thus preventing the troops from being loaded?
The sea zone is hostile. The transport must leave the sea zone in combat movement, unless other US units attack the destroyers. In any case, no units may be loaded there.