Im not completly sure because my ninja is still low level, but judging from testing after getting abandonment. EVERY PIECE OF EQUIPMENT except for weapons, counts as armor, even robes, which is uber weird. I think the game doesnt differentiate between robes and armor, only slots.

I tested having no items, then adding priestly robes, removing, then adding black robe, in both examples my def went up but my dodge actually stayed the same or went down (because they both give dodge, but one only the same dodge as my level does)

However u know there is a ninja suit right? i havent gotten it yet so, maybe that is an exception

So the answer is yes, clothing counts, but maybe ninja suit doesnt. someone needs to clarify that.

ah sorry for doubling, but i forgot to say, shield does lower your stats too, but dual wielding doesnt. (Tested this just now)

Actually, it doesn't matter. Most of the Thief/Ninja armors like Thief Plate and Ninja Suit have increadibly high dodge stats so equiping them will result in an increase in dodge rating, not a decrease.

Any armor - even the pieces specifically designed for Ninja - will negate the bonus from the Abandon skill. Since no armor means no stat bonuses, Abandon is arguably the most useless class skill in the game.

Making effective use of the skill means sacrificing all utility and damage-dealing potential of the class.