Finally got my SATA+Power extension cable, so I could test the HDD in the NVRAM's port, and it worked.
So then I plugged the NVRAM into the HDD Caddy's cables, nada. Wasn't surprised. Looked around in the BIOS some more and BAM. SATA1 - DISABLED.
Dell, if you're reading this, maybe on the page in the BIOS where you list the detected HDD's, if a port is disabled, rather than saying "Not Detected" just say "Disabled" :p
So now I feel like an idiot, but it works lol