Yes, your inmate must dial the new InmateAid number. That is not a technicality, it is the entire mechanism behind how the discount works.
The price difference on inmate phone calls is determined by the number being dialed, not by the account or any setting on your end. Phone carriers at correctional facilities charge different rates based on the destination number, specifically whether it is a local call or a long distance call. InmateAid assigns you a number in a local area code relative to the facility, which triggers the lower local rate rather than the higher long distance rate. If your inmate dials your regular number instead, the carrier charges the standard rate and the discount never applies.
The new number forwards directly to whatever phone you designated when setting up the account, so the call reaches you exactly the same way. From your end nothing changes. From your inmate's end the only difference is the number they dial.
Getting that number to your inmate as quickly as possible is the priority. A letter through InmateAid is the most reliable way to do it, and InmateAid can provide a coupon code for that notification letter at no charge. Once your inmate has the number written down and added to their approved call list at the facility, the discounted rate kicks in on every call from that point forward.