Sort of probably, but not in full.
Demo was supporting shifter in different modes (H-shift / sequential), determined by the shift-characteristics of particular car. For instance, model with sequential-only gearbox equipped in RL couldn't use H-shift.
Also, clutch was "kind of" supported, since the game recognizes it has been pressed, but it does not calculate it into shift-time.
Notice that info on offical site does not list G25 among the supported wheels, but you can be pretty sure it will work flawlesly besides the full-clutch support.