http://www.ycombinator.com/ethics/
I'd argue these four bullet points are relevant:-- Treating co-founders and employees with fairness and respect.
-- Not behaving in a way that damages the reputation of his/her company or of YC.
-- Keeping your word, including honoring handshake deals.
-- Generally behaving in an upstanding way.
The OP made a serious accusation against a YC company. I assume YC can pretty easily figure out which company this is. I would expect that YC would investigate and take action if warranted.