Yes, many coverage plans include preventive exams by either covering a percentage of the cost, or covering a pre-established dollar amount.
If the pre-existing condition is current (like Diabetes, High Blood Pressure, etc.), no insurance company will cover those conditions. They will approve the overall coverage but exclude any coverage that involves the pre-existing condition. If the person had some type of condition, which they no longer have (kidney stones for example), they do consider waiting periods. This can only be determined once the Insurance Company receives the application, and their medical team evaluates each case. In cases like these, they ask for the medical report of when that condition occurred. If it was many years ago, and there is no way the customer can get a copy of this report, they have been known to make exceptions and waive this requirement.