For the sake of argument though, would telling the landlord the tenants are smoking in the house put them in jeopardy? I would think the landlord would just, idk, give them a warning about smoking, right? Not involve police. Or am I being naive?

Yeah, you could try to talk to them in a friendly way, but would they take you seriously? Would they then be very pissed at you if you had to end up escalating it to the landlord anyway? Because to the earlier point, then they know it was you.