Generally, unless you have a contract with MIT for the use of MIT's trademarks, including the MIT App Inventor logo, you cannot use the branding in your materials.
You're welcome to make up your own certificates for participation in your program given the previous constraints regarding the use of the logo.
No, there are no formal qualifications for teaching App Inventor. Anyone is welcome to teach App Inventor, either using your own materials or materials from our website (CC 4.0 BY-SA licensed). In fact, there are many after school programs around the world organized by high school students for the benefit of their peers. There was the expert trainers program but we have not run that in some time given the time constraints on our small staff.