If app is rejected from App Store, is it possible to have a refund for Developer Program?
In general, there are no refunds of the Apple Developer program yearly fee.  I've been in the program for several years and I've never heard or seen a refund given because an app was rejected.

The reason being is that all app policies are public and available for you to review prior to determining you want to pay the fee and submit the app.  I would recommend that you do that first and see if your app idea is viable.

Just because you think the app will be accepted doesn't mean Apple can't reject it later for whatever policy they think you violated.  In that case, you can always contact Apple and appeal the rejection. 

I don't know if the 7-day cancellation you mentioned would be applicable in this case because you're not making a product purchase; you're paying a membership fee.