I assume since he posted in the PhotoKey help forum, and he has PhotoKey registered, that he is using PhotoKey.
PhotoKey's basic function is to combine images into a single composite, so the answer would be yes, but that is somewhat dependent on what exactly you mean. PhotoKey combines a foreground image (greenscreen) with a background image in most cases to create a single picture. It also has a third layer for importing overlays with alpha channels.
If you are referring to using more than one greenscreen image, then the answer is still yes, but it requires a little more work on your part. This video
explains the process.