North Korea has had surprisingly close ties with various African states going back to the Cold War and NK mercenaries have served in Syria, Uganda, Zimbabwe, Zanzibar, and South Africa in the relatively recent past.

NKers also have an active role in state-sanctioned smuggling and piracy. I think you’d be surprised how much combat experience they’ve accrued.

And they’ll still be the most experienced combat troops Putin can field. At least they get lots of practice marching up and down the square.