After configuring UMP to accept e-mail addresses instead of usernames for login, by configuring the portal-ext.properties file to "company.security.auth.type=emailAddress" instead of the original "company.security.auth.type=screenName", you cannot create new Account Contact users in the Account Admin portlet.
The portlet will throw an error that the First Name and Last Name fields are required, but you will not be able to access these fields and they will not accept text input.
This is the result of an issue with the AccountAdmin portlet.
A hotfix (ump_accountadmin_8.5.1_HF1.zip) is available which resolves this issue.
The hotfix and instructions for installation can be obtained at the UIM Hotfix Index Site.