I've created several combination MOBI/KF8 ebooks containing embedded fonts using kindlegen, and the azw3 file produced with Mobi_Unpack's splitter utility always performs exactly as expected. The embedded fonts work fine in the .azw3 files (just as they did in their respective combo file). Unpacking those .azw3 files results in ePubs in which the fonts are properly manifested in the OPF, and the embedded fonts are displayed properly when using ADE.
If you do upload a test file, be sure to upload a kindlegen-produced, combination MOBI in which embedded fonts are working the way they should (in the KF8 portion) before splitting.
Last edited by DiapDealer; 04-26-2012 at 08:02 PM.