Clethodim and Butyrac 200 should be sprayed separately with a day or so in between spraying. This is according to Keystone Pest Control website where I buy my herbicides. I do not have first hand experience trying to spray together. I spray separately and have great results. Good luck!
You don't ever want to mix different sprays unless it specifically says that you should or can. One is that they could affect the performance and the second is you could potentially have some chemical reactions that could be really bad. Let us know how it works out and take before and after pics if you can!