There's actually a lot of debate on the value of venting crawlspaces these days. Best practice now seems to lean more toward insulating, sealing, and conditioning the crawlspace rather than venting it.
I've never built a house on stilts, but I'd be inclined to close up the bottom and treat it the same as if it was a wall.
It is more about code and best practice where the house is.
I know that Canadian code specs poly in the walls, or did, or still does? But south of the border we don't use it at all in walls or ceilings. We do have vapor retarders like the faced fiberglass but that's about it on the inside of the house. I guess the movement is now to stop the vapor at the outside of the house and then to prevent the differential that could cause condensation inside the walls.