I would like like to know if I can travel back to Blackwater to find the hidden money Dutch and the gang hid?
Just be patient and play.
Based on how you wrote your question, I'm assuming you're still in the early or middle stages of the game.
I don't want to spoil the story for you, so all I can say is that the game will drive you to points where you'll have to go to Blackwater multiple times and that the money that they have stashed on Blackwater will be addressed by the gang at some point.
Another thing I can say is that you cannot have access to this money while free roaming by yourself (unless there's some cheat or bug that I'm unaware of).
It's virtually impossible to walk into Blackwater without being killed if you're not in a mission that requires you to do that. While in these missions, the game will tone down the automatic tracking that causes NPCs to find and kill you.