No. As of October 4, 2017, ShippingEasy no longer supports using an Endicia account created outside of ShippingEasy.
What is Endicia?
FAQs: Migrating to a single Endicia account
How to: Open a new Endicia (USPS) account for free
What rates does ShippingEasy offer on USPS shipments?
How will my Endicia postage purchases appear on my credit card statement?