Summary: Yes, you will have to re-enter information you may have previously entered if you are a registered developer on the Amazon Appstore.
Merch by Amazon uses a different system than our developer portal, so all users will need to enter their bank account and tax information into the Merch by Amazon site. To get started, log into Merch by Amazon: https://merch.amazon.com/dashboard and select My Account. There are three areas to complete: Company Profile, Payment & Banking (with your bank account for payments) and Tax Information.
More information on filling out the tax interview is found in the Merch FAQ: https://merch.amazon.com/resource/201846470#taxinterviewquestions
Keywords: Merch, tax ID, payment