As a rule true FSX planes can not be used in FS9. Has to do with the modelling and different texture files that FS9 can't handle. That means that none of the planes that came with FSX can be used nor can you use any plane specifically made for FSX.
Yes, it should work. Some has a folder for fs9 and fsx My advice is. Try it out, but keep the stuff you install, effects, gauges aso, so you can delete it again if the ac is bad