Yes, I was able to add all but one disk after removing partitions. If took a few steps, but eventually I was able to configure scratch to /tmp/scratch, and the scratch config survived a reboot. We send syslog to Log Insights, so the relevant parameters are:

ScratchConfig.ConfiguredScratchLocation: /tmp

ScratchConfig.CurrentScratchLocation: /tmp

Syslog.global.logDir: []/scratch/log

Syslog.global.logHost: udp://loginsights

I could not find a way to completely zero out ScratchConfig.ConfiguredScratchLocation and /etc/vmware/locker.conf. There are still log files being written to /tmp/log, which concerns me somewhat given that I want to preserve the life of my USB drive as much as possible.

After a reboot, deleting the VMFS that previously was busy worked, and the disk could be added to the pool of VSAN devices.