Constance Zimmer (UnREAL) will recur on Agents of SHIELD season 3, starting from the premiere as the head of a government agency that is hunting down Inhumans. Her character is described as 'more than a match'for Coulson.
Blair Underwood will reprise his role as Dr. Andrew Garner , a neurologist and forensic psychologist and also Melinda May's ex-husband (possibly in multiple episodes).
Source #1, #2, #3