The drives that have the most trouble are the ones that normally will not allow a partition to be put on the disk, like Iomega's line of drives. For the Iomega drives to work with removable HPFS, I recommend using the OAD driver supplied by Iomega. This driver can only be used with the SCSI controller that Iomega markets with the drives. Other controllers require use of the FLT driver from Iomega. The FLT driver, used without a driver called Lockdrive, won't allow the removable disk to be seen as a fixed disk by OS/2 and thus prevents the disk form being formatted with HPFS.
The Lockdrive driver can make OS/2 think that a removable drive is really a fixed disk. This may allow Iomega drives to be formatted with HPFS when they would otherwise refuse. A lot of people have trouble with this -- I hope Lockdrive helps!
For anyone who would like to try, there is some information from Kris Kwilas that might assist setting up Jaz (and Zip?) drives using SCSI controllers other than Iomega's. I don't know if it will help make HPFSRem work on these drives, but it might be worth a try. The information is after the section on how to make NT 4.0 use HPFS.
Other problems have been reported with SCSI controllers, like an Adaptec SlimSCSI with an EZ135 that generates peculiar errors (HPFSRem works anyway), but most of the troubles are with Iomega drives.