Are you trying to ask if this could be tortuous interference with a business relationship? Or if Snip.ly would be liable for libel/defamation of their users by

Are you trying to ask if this could be tortuous interference with a business relationship? Or if Snip.ly would be liable for libel/defamation of their users by SiteA whose page was Snip.ly'd? The former, possibly depending on the ToS of the site and how creative your lawyers can be. The latter, probably not; see 17 U.S. Code § 512, aka Safe Harbor for online posts.