You buy what fits into your training. If the school/ trainser uses Nikon as their main gear, then it will be easier for you to match it so that you can sync with the teaching.
It is not about professional brand, it just a bunch of people that you happen to meet. Can't expect the trainer to use Nikon one moment, switch to Canon the next second and then Pentax right.
While I don't know about Nikon academy but it did say "Nikon", so you should rightfully wear the appropriate uniform. That's my own expectation.