If I say Electrum can Bitcoin Core kick me from the campaign rightfully?
Yes they can, and probably should.
I see your point, but I feel like things are a little mixed up here, there is a huge difference between telling someone "what to say-- what not to say", Icopress would be in the wrong if he said
"Users who don't recommend x wallet would be removed"
or
"You have to post in the ann thread every day to get paid"
These things are against the forum rules, and this is where the forum rules end as far as signature campaigns are concerned.
Things like
"You shouldn't be recommending y wallet when x wallet is paying you to advertise it"
is pretty reasonable, and is not against the forum rules, you may call it whatever you want, but it's not against the forum rules, and it's within the boundaries of real business, if I was paying Icopress to manage my campaign and I see him pick users who recommend other competitor services I would be mad at him, I want the best results for the money I spend, what the users feel shouldn't be my problem, it's only business.
If I see someone wearing x wallet, and goes to recommend y, z wallets without mentioning x, I would think that x wallet team and their ad campaign are dumb as fuck and probably their whole product is, not because they didn't "force" that user to recommend their business, but because they picked someone who is so incompetent to advertise for them.
The real question however is, if Sparrow wallet had a running campaign with a much lower pay rate, would said user join that campaign instead? pretty hard to tell, personally I wouldn't like to be in a campaign where I am told what to say or not say, but out of respect to the people paying me -- I would not recommend competitors without recommending them, despite the fact that I have also stressed on the difference between advertising and endorsement, it's only ethical that you don't advertise for a competitor.
If the service you advertise sucks to the extent that you can't even recommend it -- you are in the wrong place, and you are just desperate for money.