In order to be successful in a gambling signature campaign you have to know gambling as many of them need as a requirement that many of the posts to be made in the gambling section.
Therefore you have high chances to be accepted in a gambling signature campaign if you are a gambler with experience.However I dont think applicants who start gambling only to be accepted in a signature are not the best ones and this is not a proven record.
Oh! finally you've said it. This is what I've been thinking too. Well, its good they wanted to be a good poster first before joining a campaign. However, I think there would only be few people who would start gambling first just to be accepted in a campaign. I hope they're not spending too much just to be in campaign, LOL. I think a lot would try to join the campaign first then learn gambling later because of the discussions here.
And just like what you've said, I also agree not all who are part of a certain campaign really contributes well in the gambling section.