I have used Caffelatex on my Shimano Deore XT wheels for 3 years with no sign of corrosion on the rims.
Unless the XT rim alloy is different than the DA it points to Stan's sealant causing this corrosion. On the other hand the alloy used by Shimano should not corrode from a sealant.
However, as mentioned previously, Stan's sealant does an excellent of sealing punctures.
YannisG