yes

> should we presume this was strategically ordered by upper management and not just someone at the location just assumed outside material wasn't allowed?

They don't even need to do that. It's far smarter to set a policy forbidding that, then set up the incentives so some lower level guy feels a lot of pressure to break it. If he does, he's your fall guy. That way you can have your cake and eat it too: unethical conduct to support your objectives, muddy enough waters to shield you from blame, and a nice little PR show about how ethical you are and how much you care.

We should presume everyone in management has perfect knowledge of all the rules in play, and that everyone voting on unionizing has no idea what is going on because of some pamphlets which have been removed.

part of executive responsibility is training your staff on how to perform job duties in compliance with the law.

if they weren't strategically ordered to break the law, they were perhaps strategically not ordered to not break the law.

erroneously or maliciously, the law has still been broken, and the organization bears responsibility.