If the provider is a Medicare provider and it's simply for a non covered service then yes, you can obtain a denial. However, if it is a specialty that Medicare does not enroll then no, you cannot submit to get a denial. We have gone thru this in the past. For example, Medicare does not cover acupuncture and does not enroll acupuncturists. So if the provider is an MD who also is an acupuncturist (we have that) then the claim can be submitted and Medicare will send a denial. BUT if the provider is only an acupuncturist then they cannot enroll in Medicare and therefore cannot submit a claim for a denial.
It sounds like you've done everything right but still are hitting a brick wall. I believe the issue is with BCBS though. They have to accept the fact that if the provider is not enrolled in Medicare because Medicare does not enroll that provider type then there is no way for you to obtain the information from Medicare. It's not like a commercial carrier where you can submit the claim even if the provider is not enrolled and get something stating it's not covered.