Well, they are on the Lore Team. So, I would say that they are working for SEGA. Not literally 1001% of their time is SEGA of course, I know that Ian's currently and has been working on some stuff that isn't SEGA related, for example, but he is hired into a SEGA team, internally.
( Also, when someone asked Ian about why the Lore Team was formed in America, and not in Sonic Team, Ian responded that he can't say the whys or hows of that, because he isn't a part of the Japanese branch. Presumably, then, from how he worded that, he's saying he's not a part of the Japanese branch of SEGA, with his wording indicating he is a part of some branch of SEGA. )