While both can influence decision making - I think greed and risk are different. Greed tends to be seen as a character trait of a person that allows him to make self-defeating decision for something that is completely uncertain - the motive can be wanting to get a quick and big return. Risk is different - one can at least consider risk wisely and with different tolerances. Rational risk-taking allows one to make wise decisions - even if the outcome is uncertain, but the impact is not as significant as greed.

I believe that both have different motives and wise risk-taking tends to prioritize long-term results with high rationality. Greed is a form of coercion driven by the desire to get a lot of returns without considering too much high risk - not even supported by mature analysis and evaluation of what consequences can occur.