@george1421 Working through chat and with Tom’s help we’ve come up with this chain command that should work from the FOG iPXE menu: chain tftp://<SCCM_Server_IP>/SMSBoot\x64\pxeboot.0
So the idea we came up with is to create a menu entry in fog to call the sccm pxe boot instead of doing it from the sccm end to call fog boot.
Once the OP has the pxe booting into FOG setup, he can use FOG to either default or fall through the FOG iPXE menu and chain to the sccm pxe boot by setting the sccm chain menu as default or just use fog as normal and leave the menu entry to select sccm boot if that is required.
The key to getting this setup to work was getting the proper path on SCCM to the pxeboot.0 file.
The OP is going to continue to test this setup, but the preliminary test was successful.