You don;t say what the subfloor is but National Wood Flooring Association guidelines, used by all mfg's, state you must have a vapor retarder between the subfloor and hardwood. See complete guidelines at my website. www.decker-consulting-inspections.vpweb.com

Yes, there should. For hardwood, we used tar paper underlayment.

For tile floors you need cement board or (my preference) Ditra. These serve as a substrate to keep any movement of the wood subfloor (which will expand/contract with temperature) from transferring to the tile and cracking it. The only exception to this would be if they're doing a full mud bed, but that's pretty rare anymore.