If you are bolting down to a concrete floor, yes. If you are bolting it to a wooden floor, no technically, but for all intents and purposes, yes, it still is.
It really depends what the UL listing says as to what the fire rating is. Most small safes are 1/2 hr at 1200 degrees.
If the fire started right below the box, the heat may be transferred inside the box by the bolts but otherwise, there would be no appreciable difference.
As far as government regulations, if it were a GSA approved container, nothing would reinstate it's rating, short of a new box.
KK