I have a very small system. I can perform HSM BACKVOL DUMPs for all of my volumes and stack them on a single SDLT tape volume. I have two SDLT tape drives; but no autoloader and no operator. I cannot seem to make HSM ask for anything but a PRIVAT tape for the DUMP. This is more or less unworkable for me - no operator, no autoloader. I have used ADDVOL for the SDLT tape(s), have AUTOREUSE, and SELECTVOLUME DUMP(SPECIFIC). If it would ask for the ADDVOL tape specifically, life could go on because the tape would already be mounted before I left work. (I do this already with DFDSS dumps succesfully because they use JCL and ask for the specific volume I have already mounted.
I also have TMS(CA1), I am not sure if this is somehow interfering with things. I have used standard 3490 tape dumps (with autoloaders) for years but it takes about 30 of those, instead of 1 stacked SDLT tape.