I agree, that a viewer or other PCB tool importing gerber data should be able to import any possible format. Gerber data are either imperial or metric. Inch or mils within metric format is just a matter of the format options, you can either have different number of fractional digits in integer format or decimal. Viewers are able to guess many format options correctly, but sometimes they need some hints. For drill data, also the format of embedded tools tables may need a specification.
Of course, you can set most format options of your choice in the PCB tool's post processor. I presume, this also applies to Pads.
Another problem may arise with tools, that don't use consistent referwnce positions for drill and gerber data, or more exactly, don't use them without user action.