This is empty gesture, just a symbol of Belarus serfdom. Russian army was already free to enter Belarus using any convenient reason like military exercises so status quo hasn't really changed. Russia might keep nukes in Kaliningrad Oblast so from the security perspective nothing major had changed.
I would not be so quick to dismiss it. Belarus claims that it still is an independent country. If it uses a nuclear weapon then it cannot be treated as if Russians used it directly. At least in Russia it would be easier for propaganda to push the story that Lukashenko did it.
What!? Of course it can, and would be. This isn't a game. Nobody cares about tissue thin fig leaves when it comes to nukes. Belarus has zero ability to make its own. Any nukes it uses that came from Russia would be completely Russian responsibility. If it cooperated that might earn it a few nukes back amongst the thousands aimed at Russia but that's it.