on the one hand, you don't have to use the insecure passwords for authentication, but you can still use it for demographics.
(Yeah, read it again.)
So what to do to create the users?
create a spreadsheet from the insecure data and use it to create a batch of addCustomerUser.pl...
bin/
otrs.AddCustomerUser.pl -f
FirstName -l
LastName -p
password -e
emailaddress -c
CustomerID (email address or something else)
username
then copy the result to the command line.
not *perfect* in the sense of password *sync* but will get the job done.