The US embassy site includes the following:
Under United States visa law people who have been arrested at anytime are not eligible to travel visa free under the Visa Waiver Program(VWP); they are required to apply for visas before traveling. If the arrest resulted in a conviction, the individual may require a special restricted visa in order to travel. The Rehabilitation of Offenders Act does not apply to United States visa law. Therefore, even travelers with a spent conviction are not eligible to travel visa free; they must apply for visas.
Thus I suggest you contact the embassy to get the definitive answer