Hi,
You should be able to implement Interstitial and Rewarded Ads into your app, however, you can't show them at the same time since they are both full screen ads. You may refer
here for the guidelines when implementing AdMob Ads to your app.
However, if you are using an unsupported platform (e.g. GameSalad) to integrate AdMob Ads to your app, then please note that we can't ensure to you that all of the features of AdMob will work as expected. It's better to contact the developers of GameSalad to check if your implementation of their tool is correct.
On the other hand, for testing purposes, if possible, you may check
our Unity sample app to see how Rewarded Ads and Interstitial Ads are implemented together in a single app.
Regards,
Ivan Bautista
Mobile Ads SDK Team