I think we have a precedent here where the campaign manager is openly policing (to a small degree but still) the content of the posts by telling participants what they can't post, or what they must include (i.e. you can't say you like product X without mentioning product Y).
This isn't new. And it's not a Meta "problem", it fits better in Reputation or Service Discussion.
I've seen a campaign manager complain about posts in spam megathreads. My take: just don't pay those posts, but you shouldn't tell someone where he can or can't post.
I've seen demands not to discuss the Russia/Ukraine-situation, because the service wants to remain neutral. Bitcointalk
allows this, as part of it's mission to be as free as possible. Just like Bitcointalk allows users to choose which campaigns to ignore. I wouldn't want to be in a campaign where the campaign manager tells me what I can or can't post. I'm totally fine not getting paid for posts that don't qualify, but I am not going to adjust my posting based on the signature I wear.
TL;DR: I don't see a problem here. It's a free market. If you don't like it, leave the campaign. If the campaign manager doesn't like it, don't pay for the posts or remove the user from the campaign. It's not a big deal.
when you say "I recommend" and list several similar wallets, then I believe that mentioning a project that spends resources on the campaign is an issue of ethics.
Can you link to the post in question?
I think Hatchy has a point: this sounds like someone who has no idea what he's advertising. I saw another one recently:
You're advertising a "private Bitcoin wallet" in your signature, but your posts make it sounds like you have no idea what that means.