Everyone who signs an AEA contract is responsible for making sure they themselves, and the producers, and their fellow actors, are following AEA rules. The whole point of signing a contract is that it means we’re agreeing to play together by a standard set of rules as laid out in the rulebook, and we get specific protections/benefits through that. The SM is usually the most familiar with the rules. The deputy is appointed to keep a paritcuarlly sharp eye on rules for their production.
Now, I don’t know anything about right-to-work laws. If you actually signed something saying you’ll follow AEA rules, than it seems to me you should do so. If you just signed a contract involving dates and times and pay, and it happens to be a production where others are under an AEA contract, I guess you’re off the hook. But if you know an AEA person is being asked to do something against the rules, it still seems to me that pointing that out to them would be the right thing to do.
In the examples you mentioned, I do think they SM should tell the producer, director, and actors what the rules say if it looks like they’re about to be violated. I don’t think you have to be the police, and insist on seeing the contract riders. But you should make sure the actors in particular understand their rights and responsibilities. Sometimes the actor may make a conscious choice to lend a costume piece for free, as a personal favor to the designer or PM or something. I think that makes it harder for the next actor to get fair compensation, because whoever they struck the deal with may insist most actors don’t really get paid according to the book, and there's the slippery slope to how rules become meaningless. Letting actors make set moves without compensation would make me, personally, very uncomfortable, so I would call Equity on that one if discussions didn't work, even if the actors weren’t concerned about the violation. Where you draw the line between informing people of rules and reporting them in some way for not following them is the tricky part where your own judgment comes in. It’s like thinking driving over the speedlimit isn’t a big deal, but having a small child ride without a car seat is wrong. Sure, we should follow all rules/laws, but in practice it doesn’t always happen.