I don't believe that is a desirable thing to do. The two products I believe need to be on the same server in order to integrate well.
If you're having performance problems, I would guess its because of your database server(s). How is your current environment structured?
Do you have a separate SQL server for the NPM instance? Do you have a separate server for the NTA Flow Database as they suggest? What are the specs on these server(s)? How do you have your storage set up on the SQL and NTA flow storage database server? How many nodes and such are you monitoring? How many interfaces with Netflow?
Correction on my part. I'm trying to move the NTA Flow Database to a separate server. My environment has the SQL server running on a separate physical box and NPM instance on a VM. I did not have a separate VM to move the NTA Flow Storage to at the time so it is running on the same box as NPM. That's what I'm trying to move over. I probably should correct the title of this discussion.