There are lots of different definitions of what an add-on is, what a rebuy is, and now what a re-entry is. The first definitions I understood were that an add-on was buying more chips while still in the tournament, and a rebuy was buying into the tournament again after busting out. Then there were certain rules that began to blur the lines between them. For example, one could rebuy before being busted out, which sounds to me a lot like an add-on. Now we have re-entry, which is a rebuy where you have to be busted out, which sounds a lot to me like just a rebuy.
Regardless of how you define them, the TD has settings that conform to any of those definitions. For example, you can select to "allow players to rebuy when they are not busted out of the tournament" right on the Game tab. When rebuys are enabled and a player busts out the TD asks if they want to rebuy right away, thereby keeping their current seat. If they don't want to rebuy right away (or they don't want to keep their current seat), you just respond "No" and then rebuy them back in later, which will give them a new seat.
Call it a rebuy or a re-entry, it's the same thing, and it is possible with the TD.