The Zipline Drop rules state: "The zipline drop is specific to dropping conventional foot- or jump-based infantry units and battle armor from an airborne VTOL air vehicle." As such they would seem to be the correct rules to use if you want to deploy infantry from a moving VTOLs.
The other option is to disembark the infantry from VTOLs after landing using the Transporting Infantry rules.
The VTOLs & infantry would be harder to hit during a zipline drop the tradeoff being the infantry become vulnerable to scatter & damage if the drop roll fails. Transporting infantry is also part of the standard rules set, Zipline Drop is an advanced option.