One step is migrating NCM from the standalone server to the Orion/NPM server. Another step is migrating device templates from disk to the database.
The latter step is done during the upgrade to 7.4. But if you upgrade from 7.2.2 directly, 7.4 (being installed on the Orion/NPM server) won't see the device templates on the other server (7.2.2).
Anyway, if you don't have an enormous amount of custom content, it' probably more efficient to upgrade from 7.2.2 to 7.4 and copy/import the files manually.