Buffs in Open Topped Vehicles

Apologies if I'm the millionth person to ask ...

if a Haemonculus is embarked on a Venom, does it get the extra toughness? Or does he have to be running along beside it like the Flash?

Yes, they have to be outside the vehicle for the aura to be in effect.

Yeah. Figured.
I guess disembarking at the appropriate moment is best then.

That or doing the opposite. Start the haemonculus outside if you fear going second, then hop him back inside and take off on your first turn. This if course depends on if your opponent is fielding snipers, heavy deep strikers, etc.

WHats worth remmeerbing is that any unit inside a Transport counts as being off the board. It counts as not being in play at all, with the only exception being the Open Topped ruke.
But Open Topped does not speak for abilities - only shooting.