Hi Rick, removing the MBR should be good enough though ideally is zeroing out the first few sectors.
Understand that OS/2 needs CHS partitioning with the cylinders ending on a boundary as well as LVM info on the drive. While Gparted should be good enough to wipe it and IIRC, it also has an option to do CHS partitioning, it won't do the LVM stuff and often will leave the drive with a hanging partition as far as OS/2 is concerned. The 256 GB size should be fine, you could make one 256 GB partition but usually better to have a couple. Need to use JFS for your file system.
Still the installer should see the drive and, with wiped MBR, offer you the chance to partition and format. You could try booting to the maintenance thingy on your USB stick and using the disk tools to partition, forget the proper name right now. Otherwise perhaps the AHCI driver needs some special parameters and you might be best opening an issue with Arca Noae.