Well, I would never participate in such campaigns cause most cloud mining sites are scam and darkstar I am sorry to say but avoid such sites.
Yeah you're right but I guess this service is different, I saw it in their thread, they are all transparent in this service, it looks good there but I'm not encouraging that you try this service I just say it for my opinion.
I do not look for a registration form and list his participation? and how to payment systems, whether through BTC wallet or wallet pow88?
The list of participants is not posted yet but I'm sure OP will post it after getting some enough participants for this canpaign.
And its not stated in the OP that you have to use pow88 wallets, so it's obvious that you have to use your personal wallet or any btc wallet that belongs to you. And yes I don't see any registration form in the site maybe OP will link it later.
EDIT: I found it here
https://pow88.com/reg.php