I tried to see if you do Digistruct peak in normal mode and when finishing it will say you have unlocked op1. I saved and quit went on UVHM and pressed continue but the op level wasn't there
mmathews comment is correct. You can go through Digistruct in all modes. But you will only unlock OP1 if you are: a) in Ultimate Vault Hunter Mode, and b) level 72.
Once you are OP1, you will unlock higher OPs by beating the run in rooms at least equal to your current OP, up to OP8.
Technically, you only need to beat the final boss under those conditions. You get the OP level and the wall of text after beating the boss, not upon turning in the mission.