I am happy to say that as of at least the FOG release on 7/24/2015, FOG installs and runs fine on Debian 8 (Jessie). Even the issue of the TFTP service not starting right after rebooting the server is resolved (by whom, I can’t say, but I know it is gone).
I have tested FOG and Debian 8 installations on existing FOG installations running on Debian 7, and on a fresh Debian 8 installation. If you are upgrading a Debian 7 installation, you will need to rerun your FOG installer (from a current GIT pull) after the Debian 7-8 upgrade is complete AND you have rebooted your server. If you have ANY software that is showing as “not upgraded” in apt-get, then your upgrade is not complete.