I'm using advanced license logging of Jazz for getting this information. It's not exactly the login report, but it shows when a user has last used a license. This works at least for floating licenses quite well.
You have to enable the Advance License Logging in the JTS Advanced Properties:
com.ibm.team.repository.service.internal.license.FloatingLicenseService
The file will then get for each license request and extend a time stamp with the userID. You know can simply search for the last entry for a user, or filter and sort it.
Example of such a license log file (csv):
Server, Start Time, Expiration Date, Policy Id, Lease Id, User Id, Operation Id, Description
https://clmserver01.domain.com/jts/, 2012-07-18T14:50:53Z, 2012-07-18T16:50:53Z, com.ibm.team.rtc.developer.floating-v3_b92a5960-cb65-11df-bd3b-0800200c9a66, _-Rzp8NDnEeGNXZb8cHYYbA, userID, com.ibm.team.reports.ide.ui.domain.ReportsDomain, checkout
