That's a reasonable way of getting a static balance, but it could be out of balance dynamically. That may not matter for a scooter.
A balancing machine at a tyre depot will provide both static and dynamic balance. It matters which rim is used for the weights.
Imagine that you have a perfectly balanced wheel. Now put a 20g weight on one rim and another 180 degrees round on the other rim. The wheel will still be ok as far as static balance is concerned but it will be out of balance dynamically because the weights will try to make the wheel 'flap' as it rotates at high speed.