If you sign up for a discount dental plan do you have to find a dentist that accepts both your primary insurance and the discount plan?

Yes, if you want to get the value of both products, i.e. the payment from your primary insurance and the discounts on procedures that are not covered by primary insurance, you need to find a dentist that is covered by both products. If you are only using the discount product for just cosmetic procedures that are not covered by your insurance, you could go to a separate dentist, but depending on the procedures it could have an impact on other treatment planning. So it is best to discuss with your regular dentist. Also, you should also disclose that you have the discount coverage when filing a claim with the insurer.