I am not a Mac person (I have seen one once), I can say that others have been able to get them to pxe (netboot) boot.
There are some additional steps required to netboot these boxes. Understand this isn’t a fog problem, but rather a Mac problem with pxe booting.
https://wiki.fogproject.org/wiki/index.php/FOG_on_a_MAC
Additional discussion on netbooting.
https://forums.fogproject.org/topic/5790/boot-pxe-macbook-imac
I also suggest that you read these threads because there are other useful tips.
https://forums.fogproject.org/topic/9278/fog-1-3-0-pb-with-mac-netboot
https://forums.fogproject.org/topic/8955/blessing-fog-server-doesn-t-work-on-macmini7-1
And finally one of the devs has first hand experience with this things called Mac, that may have some insight to netbooting these things. @Sebastian-Roth