Yes, use the LG flash tool. The T-Mobile official Lollipop update changes a few partitions that won't be backed up in your nandroid backup. Use LG flash tool and then put your nandroid on after the T-Mobile rom.
If you are flashing Fusion Rom, Illusion, Resurrection, Euphoria or the other Lollipop roms you can restore with a nandroid backup. That's what I did. I am back on 4.4.2 R after playing with the Lollipop roms.