With a self regulating system - entropy could be said to be decreasing, so hypothetically if a self regulating system were large enough (or capable of growing large enough) to take up a significant portion of the entire environment could it be said to violating the second law of thermodynamics? i.e. could a rapidly growing culture of intelligent life avert the heat death of the universe?

It would only work if their energy source is from outside the universe. Organisms can only self-organize because they have an external energy source.

If the system is not in isolation then the decrease in entropy must be accompanied by an increase in some other system i.e the environment, assuming the 2nd law. So, I'd expect the small region not occupied by your self regulating system to have an increasing entropy and moreover it would be such that the total entropy is increasing or at best zero.

 

So local organisation i.e. lower entropy is ok.

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It would only work if their energy source is from outside the universe. Organisms can only self-organize because they have an external energy source.

 

There would be heat flow between this regulating system and the environment. This would be needed to "balance" the entropy. Flow of mass would also effect the entropy.