You can use a TA to book AoA and if you plan to pay cash for AKV, you can use the TA to book that for you as well.
If you will be paying for AKV with points (either because you a DVC member or are renting from one), a TA cannot help you. All DVC "point-paid" reservations must be booked through MS and MS will only work with only DVC members.
But again, there is no requirement to book a non-DVC resort through Disney just because you want to switch to a DVC resort for part of your stay.