As far as I understand there should be no problems, because an superseding update can be installed instead the superseded. The only problem I think could be, if the clients had detected but not installed updates from another WSUS than yours - I'm not sure.
But if this would be problem think of the following: You do best practice - declining superseded updates - and after that you have to install a system from scratch (because Image fails or something else). You would have a problem with updating from your own WSUS. This I can't believe.