I'm not surprised you would need a BIOS hack. The HP BIOS is terrible, options are hidden in disparate sections and there is insufficient granularity for booting options.
I started using this about 12 months ago replacing a commercial server which was old to say the least.
BTW there is a HP server thread on the forum and another here not sure if any of those would be of any help.
Raid is not a backup! Would you go skydiving without a parachute?