With the Boeing produced 747-400 Flight Crew Training Manual in front of me, I see no references to flaps 25 with one engine inop.
With 2 engines inop:
'Maintain flaps 10 until 500'. At 500', extend flaps to 20 and begin reducing to flaps 20 speed. When landing is assured, extend flaps to 25 and reduce to final approach speed'.
Verbatim from Boeing.