Are you sure this isn't just a UEFI thing? Legacy BIOS didn't have an option to "extend" system setup menus from PCI expansion ROMs, but UEFI does. E.g. LSI SAS2/3 cards still take the legacy extension ROM and the UEFI extension ROM. The legacy extension ROM is, I guess, an independent real mode application like the firmware setup utility itself is. But the UEFI extension ROM adds its own menus to those present in the system setup utility (no doubt describing the menu structure and callback addresses in some byzantine UEFI way), and they end up looking a lot like standard menus from the system ROM.
If the configuration menus you're referring to are similar to this (shown here for a Dell HBA330 Mini, but the structure is identical to what I have at home with a Supermicro motherboard and an HBA with a SAS2008 - with AMI's look and feel instead of Dell's), then I suspect you've simply encountered UEFI option ROMs:
Entrypoint from the setup application into the device settings (notice the tip at the bottom, the HBA and NICs have expansion ROMs and the SSDs are probably being handled by a driver included in the system firmware):