My answer would be yes, with one caveat. The regulations also say that, for example, bourbon whiskey must be produced "in such manner that the distillate possesses the taste, aroma, and characteristics generally attributed to" bourbon whiskey. The regulators could use this clause to argue that the absense of any small grains renders it something else, but that would have to be tested. If, in fact, it does look, taste and smell like bourbon, that would be a hard argument to make stick.
So Chuck, if XYZ brand is made from a mashbill of 100% corn (plus some enzymes), it can still be called bourbon (if all other regs are followed)? My reading of the legal requirements is that it can.