Inkscape natively handles the fonts already installed on your PC, and can write with them using its built-in text editing tools.
The Hershey Text extension only *adds to* that set of fonts. The fonts that it contains are “engraving fonts” (by Mr. Hershey) which your PC cannot natively handle, because they are defined by the stroke width, rather than as an outline that gets filled in. These font types are so different that it is not possible (by any means) to convert an engraving font to or from an outline font.
So, to answer your questions directly:
(1) No, Hershey Text can only handle genuine engraving fonts.
(2) While you cannot print system fonts from within Hershey Text, you are *not* limited to the fonts provided by Hershey Text. Inkscape handles your system fonts directly (and in many ways better), with the “normal” text tools.
