Last night, I tried copying a conversation from comments into chat, so it could be discussed there. However, the comments didn't onebox.
A little bit of experimenting in the Sandbox revealed that the timestamp gives different links for comments when in review.* While the link works (see here), it won't onebox in chat.
Is this a bug? ...it seems that either links to comments in the review pane should conform to the norm, but I think the real problem is in chat, since all links to comments should onebox.
* In my instance, where http://judaism.stackexchange.com/questions/61682/if-a-non-religious-person-is-of-jewish-heritage-can-one-wear-the-star-of-david#comment168895_61682
is the regular link, http://judaism.stackexchange.com/q/61682/#comment168895_61682
is the link from review.