I have tried to answer this question and believe the answer is "no, robes are robes regardless of accessories". This is based on the basics of increased coverage causing penalties equal to the armor with similar coverage in the AG. Since robes are alone in their AG, there is no change to be made. I tried testing this a bit more just now by putting a guy with 0 armor use into robes, and having him swing on a critter with and without a greathelm. His RT did not change, which proves that robes+accessories is considered light leather at worst as anything beyond that would have RT penalties. (though i still believe the AG won't change with accessories and it's still robes).
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