Hi Rich,
what has been recorded in the SxS card will be 4:2:0 in the XDCAM codec, not 4:2:2.
But if you have the MXO2 (I have the MXO2 mini) you have the SDI input, so you will get benefit of that and can shoot live from the EX1 and getting 4:2:2 color space footage.
I think keying and having a better way to do color correction is the benefit of that less compressed 4:2:2 material.
Armando.