It really seems like we're overthinking the problem by quite a lot.
If you're really worried about "cruft" in the volume header, use dvhtool to list the files in the header and delete them if you know you don't want them. You can always find the "right" versions of files for your volume header on your installation media later and copy them from the installation CD to the hard drive using dvhtool.
It's very rare to need to format a drive in IRIX. I've only done it a couple of times in twenty-five years, usually by accident.

Just fire up fx if you need to repartition a drive, then use mkfs to lay down empty filesystems. If you want to be super-compulsive, partition a disk as an option disk, then use mkfs, the repartition as a root disk and run mkfs again. (This will guarantee that any swap space that might be hiding an old miniroot gets blown away.) A lot of people without much IRIX disk management experience seem to forget to do the mkfs part.
Everything you need to know is in the first few chapters of the "IRIX™ Admin: Disks and Filesystems" manual. It's really worth spending the time to learn the tools that are described there if you want to understand what is happening on your IRIX disks.
Good luck!