That's a Palm Pilot on the left, and a pink iPod mini on the right. Yes, I've been doing BGTG that long!
Moving through friendly unit is possible, but both units (the moving through and the static one) must check immediately for Morale. If the roll fails, the failing unit becomes disordered. If already disordered stay so (it is not routed).
Rout: A Routed unit immediately retreat three hexes toward its map hedge.
6.5 If the routed unit is forced to pass through a friendly unit, the latter becomes disordered or if already disordered routes.
Ok, so when doing regular movement, both units occupying the same hex (temporarily, since they cannot stack) must make a morale check, and failure means disorder (but never worse, so an already disordered unit doesn't need to even check--it's already disordered).
When a routed unit retreats through another friendly unit, the routed unit needs no morale check (it's already routed and stays that way), and neither does the unit it moves through--it disorders (or routs, if already disordered--and then presumably retreats 3 hexes on its own).
I'm also assuming that retreat paths don't have to be straight lines back toward the friendly board edge. Due to the grain of the hexgrid they can also retreat either of the two oblique directions towards that side, or combine these directions for their 3 or 2 hexes of retreat movement.