I do not think there is a clear answer, but I note that when Angel visited Tess’s family in his search for her at the end of the novel, Tess’s little brother, when he saw Angel, asked “is this the man that is going to marry Tess?” Where would he get this idea? The family had known about Tess’s marriage to Angel already. What would that imply? Maybe the child had heard how Tess was to be married again soon? Alec does not seem the type to be concerned with bigamy if he can get what he wants.
Then Angel finds Tess is in a short term rental at a seaside resort town, suggestive of a honeymoon, living as Mrs. d’Urberville, which was Alec’s adopted last name as well as Tess’s ancestral name. Certainly the use of the same name and appearance of being married would have been required for propriety's sake regardless, but it adds to the mystery.
I’m not suggesting this proves a second marriage, but it suggests the possibility?