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.
Some campaign managers does not look at this factors, some will just hire and let you do the requirement, and some campaign managers who manages gambling signature campaign even are not gamblers at all. So it depends on the campaign manager but as a participant we got the advantage here since we don't need to think long enough before making a post since we can easily relate with the topic and the conversation, we are in our field in short.