The Congolese forest are very dense and the UN has very limited capacity outside of the major cities. M23 has been very successful at taking territory and I can see how drones would help the UN monitor M23's activities.
There is no issue of sovereignty since they would be operating in the DRC at the behest of the Congolese government. The UN in the DRC has been a joke, and have not provided any real security. If they get drones that just means that they will be able to report where M23 is. If the UN took those drones over Rwanda or Uganda then they could be shot down since that would be violating the sovereignty of those countries. The mandate only calls for the UN to operate within the DRC. There are very few instances in international law where violating sovereignty is justified. From my understanding all UN gear is still the property of the country it comes from, so the UN would not actually own the drones.
The world government fears are unfortunately unfounded here.