with the absolute justice by the marine they can forget about dragon existence...
they can erase 100 years...why can't one person???
The theory is interesting. It puts Dragoon in a favorable position to lead revolutions. By defecting and his men following, it gives him manpower and i would assume the ships they had under their control. Apparently he has quite a bit of success and it couldnt be done if he didnt have the resources and it would be difficult to start from nothing. A revolutionary is different from a pirate in that it has more constraints.
Noting robin, it is highly possible that she doesnt know about dragon. He wasnt part of the bombing of her island, which some of the admirals were. His position could have been held before she became concerned researching history. Until she sided with crocodile she could have been too busy surviving and being a historian doesnt automatically guarantee a person knowing every person in a high position.