It sounds like a slippery slope to me. Where do you draw the line, in terms of the sort of information an agent is requested to look up for a passenger? If they can easily scan for names, how much further would it be to ask if someone (supplied by customer on the phone) else was on that plane? Plus any experienced agent knows that some people choose seats very carefully based on whatever strategy they might use. In other words, that empty seat is there for a reason. Should the customer service agent do something deliberate, rather than random, to usurp that?

If a customer service agent volunteers something on their own, fine. Otherwise, no, I don't think it's something that should be asked.