I got a great tip from fellow OSD specialist Oskari Kampman who had been troubleshooting OS deployment to HP ZBook 15 (and a few others) with ConfigMgr 2007. It turned out to be a known issue, here is the info from Oskari:
I managed to find the root cause for this issue. It turns out it is a BIOS issue known by HP. Currently Windows 7 deployment with ConfigMgr 2007 R3 SP2 to HP ZBook 15 in RAID mode only works with BIOS version 1.03. Versions 1.04 and 1.06 fail because partitions can't be made bootable. Other versions of ConfigMgr are likely affected as well but we use the above version.
Same issue with HP 840 G1 and 820 G1, but HP hasn't been able to provide us with a working BIOS version for these models.
– 840, BIOS versions 1.04 and 1.05 fail
– 820, BIOS versions 1.05 and 1.06 fail
Thanks Oskari for letting me know, and for agreeing to let me post this info for others to find.