Hi there!
I too am a CEP -- 25 years now -- and I sat for the CDE exam (now CDCES) in 2014. Unfortunately, there is no reimbursement for CDCESs in cardiac rehab. The care and education that you provide to your diabetes cardiac rehab patients falls under a cardiac rehab session.
Don't let this discourage you from taking the exam and becoming an expert in diabetes care and education. You'll be the go-to person when there are diabetes-related questions and maybe some compensation for your earned credential. And that's quite a nice professional boost!
Having the CDCES certification does allow you to be a sole provider of your own diabetes self-management education program and bill Medicare and third-party insurers. That's a nice feather in your cap if you want to create your own diabetes program some day and provide diabetes care and education.