there are no MEL restrictions on approaches with one gen inop.
For generators 1, 2, or 3 inop, number 4 will pick up that load bus. For #4 inop, the #4 load bus will be powered by #3 (if I recall correctly). All you lose with one generator inop is the ability to continue a normal autoland in the event of another generator (or its associated engine source) loss.