Sorry, I forgot to post the URL: http://www.macobserver.com/imgs/tmo_articles/20120906-04-MacSysInfo_1.jpg
Here you see where to get the information (model, serial number of model, ethernet vendor and device id). I just want to make sure that you have the exact same network cards and we are not talking about different things here.
Well, making iPXE work using USB has been done years ago. But with current iPXE you should be able to really network boot as well as the ipxe-devs have made a lot of progress.
One way is to configure your DHCP server properly to talk BSDP (https://static.afp548.com/mactips/bootpd.html). I have done this with isc-dhcp-server on linux but usually I prefer the ‘bless’ way. You don’t need BSDP then, just DHCP (even Windows DHCP should work). Just a day ago I had a Macmini here which wouldn’t netboot the ‘bless’-way. Maybe it’s because it had a newer firmware!? Not sure.
Before I tell you more about BSDP, please let us know a little more about your environment. Which version of FOG do you use? Is FOG your DHCP server or which other DHCP server do you use?