Nice theory, it's possible and I definitely see the foreshadowing. However, I personally don't think the Whale Tree is the Adam Tree. The reason being is that Tom and Franky both obtained lumber from the Adam Tree at separate times to build the Oro Jackson and Thousand Sunny respectively. Since the island is constantly moving, it's not like Tom could've told Franky the location of Zou a decade ago and it would've still been there when Franky went to get supplies to build Sunny. We also know the Minks don't really like humans, so it is unlikely that they would do business with them; especially not with wood from their sacred Whale Tree.
Could be though!