With WERA, yes! The E-classes. With CCS... Well, you can race it, but you'll be out-gunned in a big way. LRRS may have something. They tweek their LW rules to help real LW bikes out a bit, but I think you'll still be racing against Hawks, 620 Ducati's, FZR400's, EX500's, etc. But don't quote me.
No EX250-specific classes in LRRS. gogi- I'm not going to post parts of the CCS rulebook with regards to the LW classes here however if you know you're stupid-fast on that thing then you might be able to put up some good results at Loudon.