Google's John Mueller in a Google Hangout was seen confirming that Google will use URLs or domain names within the content that are unlinked for discovering and indexing new pages of the content. What Mueller referred to was content without an href attribute. The Google Hangout was spotted by John Lincoln from Ignite Visibility.
Mueller added that no PageRank or trust is flown from a citation or an unlinked URL. But, Google might use it for the content discovery part.Google Finds Unlinked URLs as Source to Index New Content!,