Hi,
Yes, supposing you use NCM 7.3.x, almost all NCM functionality is available in the Web. (The only major remaining part in the Win32 application are NCM reports.)
You actually don't need to add the devices to NCM via Discovery. You can use the Orion Node management page, select devices, edit properties -- say "Yes" for managed in NCM.
On the same page, you can define NCM device credentials. You can also use "connection profiles".
You should set up scheduled config backups (menu "Jobs") and update inventory regularly -- check the sample jobs to see what you can do with NCM.
Remember to use the maintenance jobs to purge old data from the DB and config archive.
Please let me know if you need more info or these seeds are enough.
Regards,
Jiri