I looked it up in the DOs and DONTs and couldn't find a rule against messaging featurees for treasuries. There might have been a rule a while ago or maybe someone misinformed me, so I'm sorry for the confusion.
Here's what the page says about messaging DONTs:
"- You must not use Conversations to send unsolicited advertising or promotions, requests for donations or "spam."
- If someone hearts your shop/item to mark it as a Favorite, that is not an invitation to send a Conversation to that person."
Here the link to the page:
http://www.etsy.com/help/article/483#conversations