Hello over there!
Even though Amazon is one of Shopify's sales channel it is, however, a bit tricky with dropshipping.
It is true that with Amazon you would need GTIN/UPC codes for your products and our supplier does not support these unfortunately.
Although people may try with workarounds, your listings could quickly be deleted and Amazon would in turn have your Amazon Merchant Account blocked as well.
Therefore I would recommend avoiding this.