Yes, but I clearly stated that said users would not be spamming or shitposting. So than I take it that it would be okay for such users.
I'm not fine with one having that many accounts regardless of what they're used for.
Thats your personal problem though.
It is highly unlikely that one has 5 accounts enrolled in signature campaigns and is creating very constructive / useful posts. Anything under this kind of quality for this number of accounts I consider shitposting.
What do you base this on? Considering that you yourself post sometimes 400 posts a month, you could easily split this among 5 accounts and enroll in 5 (different) signature campaigns. The number of accounts do not make a spammer, the post quality does.