Can entities help me with "multilevel" entity structure

I have a situation a bit like the tree registration entity example but rather more complex. In fact my "low level" entities are ponds not trees:-)

We are using ODK for internal (by staff) data gathering on ponds. We have projects which are responsible for managing multiple sites which may house multiple ponds. Assuming that we have advance knowledge of all three objects (projects/sites/ponds) and their relationships with each other then I can have three linked dropdowns in an ODK form and that works great. The question is how can I manage Projects/Sites/ponds? New projects will be added only occasionally, sites fairly frequently and individual ponds often. Adding Sites and Ponds needs to be done by project workers and not IT support.

The current system I am building is a simple website which displays three cascading drop downs, allows authorised users to edit projects, sites and ponds checking for uniqueness, maintaining relationships etc. The intention is to poke a generated csv file back up to my main ODK form using the API.

Can ODK entities do this more simply for me? I can see I could have three forms (one for each of Project/sites/ponds) but I am not sure this would give users easy visibility "in a single pane" of the full list of projects/sites/ponds and then relationships. I feel this is important so users can see no one else has added a particular pond/site/project already. Is there anyway for ODK to manage the "hierarchy of entities" in a single form with full "single pane" visibility of previous entries to assist users avoiding entity duplication?