As far as I understand the problem it is more complicated then the CFRP carbon interacting with aluminium.
If I understand stealth technology right you need to make sure you have a wing/body/tail etc without any join gaps as seen by the radar wave otherwise every electromagnetic gap will work as a radar reflector (small cavities full of corners and angels, compare with the radar reflector you put on the top of the mast of a sailboat).
In other words you need to make a electromagnetically totally smooth surface for every surface of the aircraft, i.e. you need to fill every join at least the ones facing forwards.
So you need a material to put in all the joints. I understand it to be some filling material with even silver flakes or alike mixed in to make it electromagnetically conductive at the wavelengths in question (X-band fighter radars). Pair this with the need to have something in the CFRP that makes contact with this conductive material to make it one continous smooth surface (could be the carbon or some conductive mesh in the CFRP) and you have very easily an "electrical battery" setup between the two materials leading to electrochemical corrosion.
So you basically have corrosion in every join on the airframe. Though it might not be structurally dangerous rust does not make great electrical contact, suddenly you have a F22 that gets gradually more visible on the enemy radar!
So your 200m$ aircraft is as good as a 50m$ F15 after a while, not to good