Amino groups are part of aminoacids (that's where the name comes from amino group + carboxile) a lot of aminoacids form peptides and a lot of peptides form proteins.(No question here)
Plants prefer NH3, NO2 and NO3 in that order, NH3 is metabolically easier to use for a plant than NO3, the questions, are Aminos easier to use than NH3? How fast can they (the plants) use this NH2?
I don't believe plants can use aminoacids nor vitamins directly; bacteria in the tank use this molecules (metabolizing them) and making them available to plants