Any mech with larger/oversize jockey wheel(s) will increase the total gear range - only way to find out if it's enough is to try it.
Ultegra 9s were ceramic (floating) bush top pulley, sealed bearing bottom pulley when made, the mech (pivots and general precision) is a very good unit - as durable as DA but not as many weight reductions (bolts aren't Ti, merely SS, big bits are hot forged rather than cold forged on DA). I would prefer a carefully bodged Ultegra with with bigger pulleys to a low series off the peg unit (cast big bits, sloppy pivots).
May need an extension to the rear mech hanger or major B screw adjustment to work with bigger pulleys (problem is more likely to be with the big sprockets). Should need a longer chain to take the scenic route around bigger jockey wheels.
I passed on most of my 9s bits, only things left are a DA octalink triple crank (7703, 172.5mm, 30/39/53) with worn out rings and it's threaded BB (BSA, english...), and the rocking horse shit part - a braze on 6503 ultegra front mech (that works with 6500 or equivalent double shift levers).