I would say "Involve the Inspector" on this. And ask for his advise.... Call it a grey area.... It could be considered a "wet" environment.
Location, Wet. Installations under ground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.
410.4(A) Wet and Damp Locations. Luminaires (fixtures) installed in wet or damp locations shall be installed so that water cannot enter or accumulate in wiring compartments, lampholders, or other electrical parts. All luminaires (fixtures) installed in wet locations shall be marked, â€śSuitable for Wet Locations.â€ť All luminaires (fixtures) installed in damp locations shall be marked, â€śSuitable for Wet Locationsâ€ť or â€śSuitable for Damp Locations.â€ť
Also take a shot at 406.8(A) + (B)
Other than that I would shoot for the "I'm not saying NO - but looking for a safe and suitable option" response with the GC. Technically I would look into hard-wire and fixing it to the floor - and on a GFI. Stone and certain type of tile can be conductive.
But AHJ just has to wave the hand, to say "Hey - I'm not buying that one - think again" get him on your side.... It is thier interpetaion right.... Did I say that?