Disks won't show up in the BIOS when connected through the RAID card. They are only accessible by the RAID itself. It manages them, assembles into arrays, creates virtual disks (VDs) on these arrays and presents those virtual disks to the OS and the BIOS.
To manage disks with RAID card you use the card BIOS utility or specialized OS software, for HPE servers this is usually SSA (Smart Storage Administration). I use CLI variant in Linux, so the exact package and executable is called ssacli in my case (it once called hpssacli and the ancient versions were called hpacucli, ACU stands for "array control utility"). But those HPE RAIDs don't allow to set up direct access to disks. Some RAID cards can erase disks for you, but I don't know which one do you have and how to instruct them to do so; learn which exactly card you have and read manual for your management software on how to do that.
To properly have a direct access to a disk from the OS you need either a HBA card, a RAID card flashed in HBA mode, or a RAID card which allows setting up JBOD access mode on the fly. In either case you can have a direct access to the disk from the OS and then erase it with e.g. dd. I had some success with that with LSI (then Avago, now Broadcom) MegaRAID. But not every LSI card firmware allows to do that; modern Dell PERC's are rebranded LSIs, but those I've had my hands on have a JBOD feature disabled. Again, I use them in Linux, and via CLI, so the package and executable I use is megacli. It has a successor, storcli, which I suppose must be better to use with recent Broadcom LSI-derived cards and/or older cards with updated firmware. I didn't used it myself.
