Is there a way to link up the username IDs which are included in the output with the actual usernames? 


Not at the moment.  We have both in our database and could display either one.  Or we could display the user Id on the /cohort#YourCohort page, alongside the name.  Or both.  These changes would be easy to make, just let us know how you'd like it and give us some time to make sure it's ok with everyone else.