That is the one thing FAQ didn't address and it's a major one. I'm a Zilfin player myself and here's how I see it.
1. The hitcher's wording states that the unit can hitch instead of making a normal move. So that would mean they can't hitch as the Zilfin hero phase move is for one unit only (the vessel).
2. BUT! the very next words after those are, in brackets, «as long as this unit has not already made a normal move in the same phase». Because of that, I take it as they can hitch because they have not made a normal move in that hero phase.
Now RAW, it is debatable as two separate parts of the rule could lead you to two different answers. However, RAI, it's clear that the intend of the rule is that you can't move wholly within six inches of a ship, then fly high or fly high, then move. That is supported somewhat by an «official» video of Warhammer TV when they were previewing the new book against Mawtribes. The KO player used the Zilfin move with a Gunhauler if I remember correctly and hitched a unit of sky riggers while doing so.
As a TO, I ruled that you can hitch with the Zilfin move because the hitchers haven't made a move in the same phase and I see the part in brackets as a clarification on instead of making a normal move, rather than a second condition to be met to make the move. I know other TO's rule it differently. Both could be argued. Unfortunately, only a clear FAQ will settle that debate.