Will Enterprise User IDs with a dash create a new Portal Account correctly, when you setup Portal 10.5 using the IWA with AD accounts. It appears they will work correctly by this explanation.
Add members based on existing enterprise users
If your portal has been configured with an enterprise identity provider, enterprise accounts can be added individually, in bulk, or from enterprise groups managed by the identity provider. You cannot add enterprise accounts to your portal if it has not been configured with an enterprise identity store.
Accounts must include an email address in order to be added to the portal. Any special characters in account names will be changed to an underscore (_), except the at sign (@), point (.), or dash (-).
Add built-in portal accounts
However all the other directions explaining how to setup new users in Portal using built-in, one at a time, say differently. They say you can only add user-ids with an underscore.
account—The account is the user name to be used for the built-in account. Accounts must be between 6 and 24 characters in length, and they can only contain alphanumeric ASCII characters or underscores.