Can 2 sets of parented objects be added to a 3rd parent? I'm new to Blender and I'm trying to organize my objects by creating a parenting hierarchy. 

I currently have two parented sets of objects each containing several dozen objects (children) each. I would like to combine these two parents under a "super" parent while retaining the "sub" parents. Is this possible?

I've been unable to do this myself, however my research so far says nothing about this being impossible.

Thanks.
Yes, this is possible.

Just select the parents of each individual set of parented objects and parent them to another object.  Note: it is often good practice to use empties as parents for sets of objects for this kind of application.