Alternatively to modifying the TeamPulse User Management names you can edit the sync mapping information to perform value mappings between TeamPulse user names and TFS user names. To do this, on the Sync Info screen you would expand the Remote Server Configuration section (see attached screenshot 'expand server configuration.png') and then open the sync mappings xml (see attached screenshot 'edit sync mappings.png').
Looking through the xml, underneath the <EntityMappings> tags is an empty <ValueMappings /> tag which can be filled out to map TP user names to TFS user names (this will be almost at the bottom of the document). Attached is an example of how that section might look when completed (see 'valuemappings.png').
Then you need to add an association to the AssignedTo field on each relevant entity (Story, Task) to use that value mapping data when syncing, which might look like the highlighted attribute areas in the attached screenshot 'field value mapping assignment.png' (look to the far right on the screenshot).
If you decide to go this route rather than manually matching the names between the two systems, please let us know if you have any issues and we will attempt to provide further guidance.
All the best,
the Telerik team