FS9 models will work in up to P3Dv3 so yes, not sure about the gauges though.
The only ones of concern are those in the bf109e.gau, I only see 3 that use that in the VC but one of them is the Directional Gyro.
If you have v3 installed it wont hurt to give it a try but when you install the gauges don't let it overright any of the default ones, v5 has a Magnetic_Compass.dll already so I assume that v3 will too.
I don't have v3 installed at the moment so cant check.
Although to be on the safe side I personally would put the gauge files in the planes panel folder instead of the P3D main gauge folder, that way they wont interfere with the default gauges and will be easier to get rid of it doesn't work.