It's taking advantage of another developer's $99 payment. I just took a look at one of these apps and the in-app purchase to remove ads is $1.99. I think if I did this I'd throw that developer the 2 bucks.
Sort of like when you bum a ride from someone, even though it's not costing them anything, it's good form to offer to split the cost of gasoline.
I'd pay Apple $99 before I asked another developer to do that for me, probably putting their agreement with Apple at risk.
Taking a principled stance against Apple is fine. I'm totally onboard with that. I only think it's uncool to take that stance and then use another developer's cert without their permission. Even though it's unlikely, it can only harm that other developer.
Based on all the downvotes HN seems to disagree, but I don't see what's so unreasonable about my position.
Sort of like when you bum a ride from someone, even though it's not costing them anything, it's good form to offer to split the cost of gasoline.