Can I use green cardamomm pods and ground cardamom interchangeably?
If by green you mean green cardamom pods, the short answer is yes. You will have to remove the outer green shell and grind the black seeds inside. The black powder available in stores is made from the same black seeds. It is always preferable to grind cardamom seeds fresh because ground cardamom tends to lose flavor with time. 

I get an acceptable result if I grind the seeds with a mortar and pestle.