My son spent his first two weeks in the NICU almost 20 years ago. It's a scary time!
Good luck to the little ones, as well as the parents. It's such a rough thing to go through.
As mentioned, each NICU has its own set of rules, and depending on which nurse you ask, you may get a different answer. I had started cutting squares for a flannel quilt for him before he was born, and my mom finished it in a rush to get it to the hospital. They encouraged it because it would "smell like me". Might be a good idea to let mom sleep with it for a night before taking it to the baby.
Also, when washing it, use a detergent like All Free and Clear (no dyes, etc).
As for future donations, I'm finally starting to make some myself for the NICU where my son spent those two weeks. It was always a goal of mine as they take such great care of those little ones.