I sorted this out with some help via Live Chat. Thanks!
Take a look at what is set for your "jiveURL" in your System properties. This property should be set the base URL of your installation.
The process that sends the Registration Validation Email reads this system property to put at the beginning of the validation link address that gets put into the body of the email. If the system property isn't set, the process will try to read the property from the database out of the jiveproperty table by looking for a record in that table with a value of "jiveURL" for the name column. So, you might look for that record as well.