Unfortunately it is not currently possible to sync tags between TeamPulse and TFS. It is also not currently possible to create custom fields within TeamPulse. I have added feedback votes for you for both of these feature requests.
As a suggestion, would it be possible to use Areas to help with your specific issue? This would obviously depend on your current use of areas, but these can sometimes be used to categorize items in a manner similar to what you describe.
the Telerik team