[GeoffR]

I tried it on my Glo with firmware 3.4.1:

With the epub reader the .svg images display okay, but the embedded fonts don't work. With the kepub reader I get the same black rectangles that you describe, and also the embedded fonts don't work.

The problem with the embedded fonts is simply that there is no reference to them in the stylesheet: there are no @font-face declarations.

Sorry I don't know what the problem with the .svg images is, but then I don't normally use sideloaded kepubs. I've never seen the problem in Kobo-made kepubs.

Edit: The embedded fonts worked in the .svg tables as you described, I was thinking you meant the main text to use these fonts.