Mediation is a great app which allows your original ad networks to compete against Ezoic's own ad exchange. We recommend that you add any ad networks which you already use to the Mediation app - but these networks do not need to be 'approved' for you to use Ezoic. Even so, lot of our publishers link their Google AdSense to Ezoic, and we highly recommend it, more info on how to do that here.
The approval process for AdSense can take some time - if you have signed up and joined our AdSense Certified Partner Programme, do not worry if the app is still pending. If you have not already applied for the Programme, contact your Ezoic representative.
Even then, AdSense can remain Pending until your AdSense account competes with and wins against the Ezoic Ad Exchange.