Your question has a basis that makes no sense to most of us. You never have just two choices to provide a 401(k). I think your understanding of how this all works is probably in need of some additional education. Financial firms provide INVESTMENTS, and you have hundreds of choices of investment firms. The plan design/documents can be provided by consulting/administration firms (like mine) that actually helps you set up the plan and then you can go anywhere you want for the investments. I suggest you might want to find an administrative firm that you can discuss this with. If you wish, send me your information to larrystarr@qpc-inc.com and I will try to help you find a firm in your area that you can at least speak with. You certainly do not have just TWO choices.
As to your specific questions, those are, frankly, trivial issues. SEC registration does not give you any real benefit. If a firm is required to be registered and isn't, then that's a problem, but that's not what you describe here. If the other firm is a trust company, they are regulated but under different authorities.