I'm debating the same thing... I think I would have more fun on the DRZ, but I much prefer drier trails in July than deep greasy mud pits in April.
Corpse... basically the Bethany is two rides in one. The big bike track does a gravel route and a few no-maintenance road allowances and the most you'll run into is a slight mud puddle or a bit of sand. If it is like the run I followed with Supernam last fall, you could likely do it with mostly street tires.
The dirt track goes into the Ganny, but I think it occasionally hits a road or two, so I am not sure if your CR250 would meet the licensing requirements. Once ODSC has the details finalized, I'll post up whatever they present.