Tataru might be able to find something on him, but it would have to be something "new" that makes equal sense to everyone.
In any case I think it would be a poor plot point to just get a free chance to manipulate the villain. The full extent of Tataru's blackmailing (that we've seen) is Carvallain, and that's just a neat excuse to bring an existing character into the main plot while confirming existing information. There's no tension in that event - we were going to be on a ship to the Far East anyway; that just made it a memorable one.
(Estinien too, but that was more Krile's work IIRC, and trickery rather than information gathering. And again, no real tension because of course they were going to rope him back into the plot somehow.)