Until now all of the sideloaded fonts containing kerning tables that I had tried, whether OTF or TTF, functioned as expected in the EPUB reader but remained unkerned in the KEPUB reader.
But I found that
converting the font to TTF in Fontforge with the "Old style kern" option enabled allows the kerning to work in the KEPUB reader too.
For example, I tried the Charta font from
this thread with the KEPUB reader on my Glo (firmware 3.13.1), the first screenshot is with the font in OTF format, the second converted to TTF with the "Old style kern" option enabled: