That seems odd to me as well. It would be one thing if her supervisor was running an actual research study on the topic and suggested you be a part of it. But this just sounds like they're interested in you because they haven't seen someone like you before. And I don't get the sense you said you couldn't come back because you couldn't afford it (then maybe I could see them making you that offer). So I'd try to find someone else.

Another thought: Would your wife be willing to go to marriage counselor and/or a sex therapist with you? If you could find someone who's at least a bit knowledgable about fetishes, they could probably help your wife understand more. And maybe you could find ways to integrate your fetish into your marriage. Or at least so you wouldn't have to be secretive about seeing a dominatrix.