Yes, the Harlequin Anemone Crab is reef safe. It has a symbiotic relationship with anemones, where it uses chemicals released by the anemone to find a compatible host. 
Explanation 
The Harlequin Anemone Crab uses chemicals released by anemones to find a host.
The chemicals released by anemones may have evolved to deter predators and parasites, but for the crab, it's a chemical trail to a compatible host.
The crab and anemone have a long-lasting symbiotic relationship