Yes. A license key for the SimpleGantt VBA tool unlocks the SimpleGantt add-in at no extra cost. Open More options > License on a chart, paste the key from your original purchase email and add it.
Both products use the same license, so they share its device slots. Every computer where you activated the VBA tool still counts. If the add-in says the device limit is reached, sign in to your account, remove the devices you no longer use, and add the key again.
More about the move in Upgrade from the VBA version.