Thanks for all of your responses. First, let me say that I my comments about CatDV’s lack of a hierarchical keyword structure wasn’t intended as an indictment against it. Clearly, it has extensive features and versatility. I have virtually no experience with any other products like it. Adobe Bridge is my closest reference point and that is why I drew the comparison. I realize it is a different tool for a different purpose than Bridge. I think you can see though, how a hierarchical structure might be a good thing.
If I can copy / paste a large list like the one I linked into a picklist then it may be a good answer. It is not exactly what I pictured but still good. Definitely, my aim is to limit “free form” entry fields. Can you prevent someone from entering additional terms into the picklist and force a choice from something in the list?