It's also the fault of technology (or, at least THEIR technology) that the only way they could continue "business as usual" when someone is absent is with their ID having to be used by someone else. If the issue is Outlook, then I believe their I.T. people could and should have routed the incoming mail for the absent staff member to the person covering for him/her. If the issue is broader (access to major databases) then they have a big design problem.
What an a-grade muppet, firstly I would like to say paper trail, secondly if your going to hack do it from behind a firewall/proxy so they can only identify the network where a hack came from. This person deserves the full force of the law if you ask me for being so stupid more than anything else.
To get away with a stunt like that you would need to be far more elaborate, it would be easier to get a past bright student to take the tests for you, then the paper trail would match ( I think they did that on Law and Order ).