You need read-only access for the objects that you would like vCenter to monitor.
If you're using Virtualization Manager or Storage Manager to monitor your VMware environment, you will also need Datastore browse permissions.
Let me know if you have further questions.
Thanks for the reply! I ended up finding the NPM Integrated VM monitoring document yesterday, and it says the same thing you are saying. Right now we just want to use what is built into NPM. Thanks again.