No, but you don't have to earn a commission in order to be a technician or specialist. However, you do have to develop a field of study (such as physics, linguistics, engineering) before or during the commissioning process. So, the question is this: what was Uhura's field of study while she attended Starfleet Academy? That's what is at issue here. Personally, I am fine with Uhura having a background in linguistic as a part of her duties as a comm officer, since she displayed a limited technical background throughout TOS.