Unfortunately this is not possible at present. The Netflow module utilises the managed nodes In network performance monitor.
If you really wanted to separate the two You could look at another Orion for Netflow and just move your Netflow managed nodes to that poller
This would ensure that the two are separate.
Your database doss seems extremely large. You may want to advise the Netflow group to Look at their retention setting For Netflow compressed data .
If you are capturing data From a large number of devices having the default of 90 days for compressed data will make your database extremely large and could affect performance