Then no, you don't need to be certified in any way.
However, if you need access to Dev stuff at Nintendo, they must know you're in somebody's Team, but the Company Admin will take care of this part.
The company you work in must be verified by Nintendo, otherwise you won't get any access to it, but that's obvious.
For the most of the time, signing happens Online, but sometimes, it'll happen by Postal.
That's a task for the Publisher and/or Owner, so you won't need anything to sign, other than the NDA of your company.