According to Grant Morrison's Multiversity, the Hand is used to represent change, as much as it does creation and destruction. I personally find the idea of Dr. Manhattan creating the DC Multiverse impossible to go along with. However, his experiments doing something that changes the DC Multiverse? That is something I can believe.
After all, wasn't the Hand also the hand of the Anti-Monitor during the Infinite Crisis? The Hand was also the hand of Volthoom at one point? All of which preceded a period of great change in the DC Multiverse.
This is all speculation, but I'd say Dr. Manhattan played a role in changing the DC Multiverse, as opposed to creating it outright.