Ah, the neverending quest for requirements traceability
Technically, sure you can annotate the life out of your unit tests with requirement ID's and whatnot. Whether that makes much sense in terms of cost and benefit, I doubt it. For instance, I can't even imagine the heuristics for systematically deducing which of the hundreds of features of your CRM system (for example) relate to the EmailValidator class and its dozen tests. How about that component that you use for all the buttons on your UI? Surely the tests for that component should be tagged with any user-visible feature in the system that involves pushing a button.