It's listed in the quickspecs so there must be some way to change the boot order. Presumably you have gone into the BIOS of the DL320s and checked that the RAID controller is listed first in the boot controller order.
According to the discussion here it's not possible to disable the boot BIOS on the SC11XE, you certainly can't use the shuffling the PCIe cards about trick to change the order that the cards appear since the P800 won't fit in the other slot. Perhaps there is a PCIe mapping table in the server BIOS settings so you can change the order there.
Have you got the latest server BIOS system ROM installed, there was an issue with old firmware where it didn't boot from the right smart array controller if more than one was fitted so this might affect other bootable controllers as well. Latest version is here .