This is from the Silver Sneakers page:
To become a SilverSneakers group exercise class instructor, one must:
Be at least 18 years of age.
Maintain current CPR certification.
Hold a two or four year degree in health, exercise science, recreation or physical activity related field or maintain a nationally recognized certification (for example, ACE, AFAA, YMCA).
Attend a SilverSneakers instructor training workshop for the specific SilverSneakers class one would like to teach.
So it would seem that as long as your certification is a ‘nationally recognized one’ you are good. You would probably have to contact them directly to find out how they define ‘nationally recognized’