Is a MEP with one trust to hold benefits of the employees of the different, unrelated employers subject to securities laws registration if no trust assets are invested in securities of any of the participating employers? Or is there a securities law exemption where no employer securities are involved?

A multiple employer plan is not exempt from registration even if it does not invest in any employer securities. If the plan allows employee deferrals or contributions, it has to deal with lack of the usual exemption.

Thanks, QDROphile. What about a multiple employer DB plan that has no employee contributions?

Generally no registration is required, but the arrangement should be evaluated by someone who understands the rules and issues.