Hi there!
In my experience, HP Servers usually function the best as a 3615xs with the 1.03b loader by Jun.
However, be aware that on some versions, the onboard NICs will stop working since some versions apparently only support Intel NICs.
Are you certain that pid and vid of the stick and the mac address(es) are correct and that you saved the grub before dismounting?
I know that might seem like a dumb question, but things like that were the most common mistakes that both me and a couple of friends of mine did because we were too impatient.
And last but not least, I´d recommend deleting all data on the HDDs in between installations. In case 2, DSM could be partially installed or just be corrupt and case 3 could see the data on the HDDs as an already existing DSM and therefore just try to recover the data, which fails because said data is corrupt. I hope you get what I mean...
Anyways, best of luck with your installation. If it fails again, you could try installing a virtualization OS and try it there, maybe that works.