It may well have been vectored around the ML CTR, however it had been in its own nav for about 40NM after the vectoring. I guarantee ATC will not vector an aircraft for 40NM. They were on their own nav and OCTA when the collision happened. They may well have been for the VOR, however it was OCTA.
Calling for clearance on the ground may well be your standard procedure, however it would be completely unnecessary given you don’t enter CTA until a significant time after takeoff and I doubt a an airways clearance would be given off the ground.