da man normally is in reference to "The Corporate World". This does not specifically target "Corporate America" as it is country specific if it is not taken in the global sense.
da man works on many levels of the Corporate World. the lowest common denominator is the boss that an employee reports to, to the company he/she works for, to the corporate working world as we know it.
Joe : "Hey Bob did you see that game last night"
Bob : "Nah Joe, I was too busy workin' for da man and didn't get home until it was over."