No problem, while we do not have an avatar campaign, you can use avatar from other campaigns
Nice gesture from your side, but i would advise of adding the rule that "Participants may not advertise similar or competing gambling related sites while enrolled in this campaign"
Reason is that it would be both counter productive and contradictory if someone would advertise two gambling related sites, but it's your call..
Another thing (in regards to gambing section posts); "At least 30% of the posts should be made on the Gambling section. "
Imagine scenario: 
person A posts 100 posts , where 30 of them are in gambling section (30%) - everything good , person A is eligible for payout.
person B posts 300 posts, where 60 of them are in gambling section (20%) - person B isn't eligible for payout due to not following the rule.. ?
Miranna, you made a good point. So, I will only accept avatars from not gambling related websites.
Actually, 30% of the paid posts should be in the gambling section.
Another example, lets suppose a user had 50 posts in a month and only 9 in the gambling section, I wont punish the user not paying him at all, I will count only 30 paid posts