Seems a bit too heavy handed. As I mentioned, I'd rather the Bounties section simply not contribute to the post count. Doesn't punish the legit users who are there to apply to bounties but doesn't allow the spammers to pad their post count / activity.
Why? It is strict, but very easy to *implement* and enforce. I am even working on moving signature campaign applications, of the campaigns that I manage, off of the forum.
Since quite a few campaigns use the forum to manage entries and weekly / monthly reports. And those that don't, quite often use it to verify whether a user who applied off-site is actually the BCT user he claimed to be. Sure, there's ways around it, but unless done automatically it's usually rather inconvenient to do so (e.g. accepting entries via PMs either via your main account (flood of PMs) or via a dedicated account (have to switch between accounts)).