The support with the Extreme Reactors mod does not work in the way that the bees can't be bred, they don't give their corresponding Grains and the grains can't be used.

I'm guessing that they don't work because they're still there left from the old Big Reactors support and the integration does notwork with Extreme Reactors. However, I might be wrong

It has nothing to do with the old Big Reactors support. Extreme Reactors don't register their OreDicts in the preInit event, how it should be.