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The "vdo" man page says:

       --vdoHashZoneThreads=thread count
              Specifies the number of threads across which to subdivide  parts
              of  the VDO processing based on the hash value computed from the
              block data. The value must be at least 1 and less than or  equal
              to  100.  vdoHashZonesThreads,  vdoLogicalThreads  and vdoPhysi-
              calThreads must be either all zero or all non-zero. The  default
              is 2.

The minimum value is in fact 0, and the default is 1.

The message output by "vdo create --help" has the correct values.

I haven't checked the other values yet.

vdo-6.1.1.99-2.el7:
       --vdoHashZoneThreads=thread count
              Specifies the number of threads across which to subdivide parts of the VDO processing based on the hash value computed from the block data. The value must be at least 0 and less than or equal
              to 100. vdoHashZonesThreads, vdoLogicalThreads and vdoPhysicalThreads must be either all zero or all non-zero. The default is 1.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:3094