When you backup upon import, that's basically so (If converting to DNG), the proprietary raws are also backed up to that secondary drive. Nothing else; anything 'backed up' is just those raws; no edits, sidecar's etc.
Easier, far more effective: backup everything you can't afford to ever lose using a good backup utility. The catalog, the raws, the presets, the camera profiles; everything. Knowing what OS you are using, one can recommend a backup utility, many can do this whenever any file changes automatically and do so automatically when you're fast asleep. On Mac, I use Chronosync to do this and backup to a cloud too (Backblaze).