I think most people use the IBM JCE provider. I was actually hoping others would respond to the question in case my assessment is off the mark. The IBM JCE is the one that is tested and supported. Since many of the WebSphere products are evaluated for different compliance requirements (Common Criteria, FIPS, etc.) certification depends in part on the ability to control the quality of and address and discovered defects in the JCE provider. I've seen attempts to use other JRE or JCE providers with mixed results. For the ones that worked, I'm not sure if they were supported. You'd need to open a PMR or ask your account rep about that part.