[x] As a spy, there are a lot of things you would like to find out about the White Court, many of which they would rather keep a secret, assuming that role should be more than enough to satisfy the requirements of true and loyal service
[X] As a recruiter of sorts, and an expert on white court vampires. He'll look for people (white court included) who could be trusted to be recruited by you. Starting with those needed to establish an organization you could be in charge of. He'll also help you talk with deranged white court vampires in the Underground.
[X] As an armsman of sorts, a martial adjunct. You have already seen how skilled Thomas could be against the Winter Court, he can cover this service as him doing favors to Harry
[X] As a researcher. If you are to truly help Thomas and his breathren, while probably coming in conflict with other white court vampires, you'll need to know much more of their condition than you do now. And there should be none who know more of the origins of white court, the true nature of their hunger, past attempts to affect it, than white court members themselves. He could look into such records for you.