The issue of Chiss force users has been argued a lot. If you go back to the source (Timothy Zahn's books), they really didn't talk much about it, Thrawn indicated it was something they didn't really know about, but due to the fact that there are now a couple of force-using Chiss in some novels and comics, it's accepted that they can exist. Also, since we know Chiss are descended from humans, there's a pretty good chance there are Chiss born with force sensitivity. The general accpeted idea is that they just don't teach/encourage it in their culture.
As I've pointed out before on this discussion, Chiss interacting with the Empire or Republic at all prior to the Clone Wars is total lore-changing retconning anyway.