In some campaigns, sometimes it is not enough to even be a jr member, you need to be a member. However, in most bounties, your rank is not important for any campaign other than the signature campaign
Rank for twitter or facebook campaign is only needed if these campaign pay in BTC but if it's a bounty I think you guys still can join even you're a newbie cause the only thing you need is a social network account with a lot of real followers or friends.