I have a HP DL380 G7 server with a quad intel expansion card in slot 3.
I can't seem to find anywhere in the iLO/BIOS to tell it to boot from one of these expansion interfaces - is this even possible?
We can turn on the on-board NIC's but our base OS has problems with broadcom.
Yes, it's possible. Try F11 for boot options during the POST process.
You may also be able to control this from the Intel BIOS.