All of the supra blowers that I've seen vent from front to back. I've never seen one below the engine but on most the hose either goes around the side of the gas tank, or up through a metal manifold behind the gas tank and then into the transom vents.
As far as where it's pulling fresh air from -- who cares? It should be pulling it from the front vents but as long as the engine breathes it's getting air from somewhere and it should be ok.
Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.