The Kona 3's we have can capture VANC for 708 CC on capture. The closed captioning remains fine in Quicktime, but going back to a VTR via SDI doesn't retain the CC. We've been up and down this every single way possible with all of our hardware. Retaining the VANC data between computers and VTR's is a hard thing.
In your circumstance, I think the only way to re-insert the CC on your insert edit is to use the FCP7 edit to tape with the CC file option which will require an .scc file of the that specific portion of the the closed captioning.
Senior Tape Operator/Engineer