Well my aunt's work does somthing like this, if you get your blood checked once a year you get a discount, but I don't know if the company gets a copy of the results. I would think that would violate HIPPA, but I know if you switch doctors you can sign a release so your new doctor gets the information. So I assume it's all done with your permission(Signing a release with the doctor).
America is the only country that ties health insurance to employment also.
Edit: Looks like some positions only urine tests are allowed by federal law but looks like just DOT jobs. So If you have a desk job or working retail, looks like the companies are free to pick any much any method. https://www.quora.com/How-likely-is-a-hair-drug-test-for-pre...