Veil is made of mostly of water. The surface can be seen as having a current but under that the water is more solid and slower moving.
Robio Crafts are able to skim across it's surface and even dive into the veil. However because of it's density it needs to be a straight shot.
Adjusting course inside the Veil could destroy a smaller robio craft or at the very least cause great damage to the GravGen Core carried behind them.
Because of this Robios almost never dive into the veil unless they know where they will come out, Robio crafts tend to find veins or that allow easy access from one part of the Veil to the next.
For more direct pathing through the veil a Wave Breaker is required, as they can freely move around even inside the most dense part of the veil.
The only planet to harbor life in The Veil is Sanctum which is almost in constant with The Veil