We don't collect process role information in our ETLs, so it is impossible to report on it using the DW. If you do want to report on it, you would need to run a SELECT statement against the live database, which I would advise against for performance considerations.
As a workaround, you can generate a runtime report for a project area which shows the roles assigned to users. See the following technote for more information:
http://www-01.ibm.com/support/docview.wss?uid=swg21632380

I believe there are enhancement requests on jazz.net to add this feature into the ETL collection process.