For an insurance company, your credit rating is an indicator of your financial responsibility. If you have a low credit score, you are automatically more of a risk for the company than someone with a high credit score. this means that a low gredit score could result in coverage being denied, or a requirement that you must pay higher rates for your coverage.
If you are denied coverage for health insurance based on your credit, the best thing to do is apply for coverage through another company. Employer sponsored health care does not generally look at your credit score, but signing up for group insurance through other sources almost always involves a check of your credit score. Private health insurance may deny bad credit outright, or they may impose premiums that much higher than other policyholders pay.
Whether or not any particular insurance company will deny you health insurance based on your credit score depends on the state in which you live, the company that is writing the insurance, and even how bad your credit truly is. The only way to find for certain is to contact the insurance company and make some discreet enquiries about their policies in regard to people with lower credit scores.