Can I use the "share" feature on nookColor with non-B&N content?
The answer appears to be no.
After testing a few different epub sources none of them from alternate booksellers (or public domain) were able to use the "share" option which lets you share a highlighted portion of the text with your social network. This is unrelated to the lend-me feature. Seems to be a bug or yet another special feature reserved for B&N content.