Medicare has very few national policies for coverage that are predicated on racial background. One is the glaucoma screening benefit, which is specialized for individuals who are African American and 50 or older, or Hispanic American and 65 and older (here). Medicare is silent on questions like how this is defined or how mixed-background individuals are coverd. And for example, individuals from Egypt or Dutch background South Africa are from the continent of "Africa" and now live in "America" but the coverage is silent on how their benefits would be handled.
There is no national policy that is specialized for individuals of Ashkenazi descent, but there are draft local coverage policies that would guide BRCA testing for individuals with different backgrounds. While these have statistical bases, they also raise challenging implementation questions.