A lot of top tier raiders have told me that accessories don't work in defence, while others tell me otherwise. I don't know which side to believe, as both sides claim to have tested it. For active gear, it clearly says that it is not used in raid defence, but that disclaimer is not present for accessories. When setrting up defences, the stats of accessories are shown, which leads me to believe it is used.
I don't believe CAG has ever confirmed this or not. I highly urge CAG to do so as soon as possible.