According to Western intelligence, yes. North Korea has sold Russia millions of artillery shells and rockets during this year, seemingly to make up for production shortfalls in Russia itself, relative to the demands of the fighting. (Mind you, there's no claim these were provided gratis.)
According to declassified intelligence obtained by the New York Times, Russia has bought millions of artillery shells and rockets from Pyongyang.
There's little detail to those claims provided in the press, though. And both North Korea and Russia denied any such NK to Russia ammo exports took place or are even envisaged.
As I don't see this mentioned in other answers, the same report mentions Iran selling military drones to Russia. Those have been somewhat better documented with photos of visits to Iranian shows and seemingly cargo transports from Iran,
but I've not seen reports of them downed in the field in Ukraine, for instance.
According to LA Times, Russia has acknowledged that North Korea has offered workers to rebuild the Donbas:
Russian Deputy Prime Minister Marat Khusnullin has said that North Korean construction companies have already offered to help rebuild war-torn areas in the Donbas and that North Korean workers would be welcomed if they came.
The Guardian comments/claims that would be in
breach of a UN resolution that required member states to repatriate all North Korean workers from their soil by 2019.