The Oran’taku is a species introduced in the Star Trek: Enterprise episode, “Rajiin“, where they encountered an Oran’taku spy tasked by the Xindi to steal biometric data. They are telepathic, and are able to mesmerize their targets (often seductively), then run their hands over the parts of the body they wish to bio-scan.
As an Enterprise era species, there is a lot of leeway for what happened with the species. They could have joined the Federation, or remained independent. They would be an interesting addition to Starfleet, although the way they mesmerize their targets needn’t be seductive (as portrayed by Rajiin). A Starfleet Oran’taku likely would need to seek permission before using their power on another.
They would also make excellent free agents working against your heroic crew.
Oran’taku (PDF)