The answer is : "Copper member is not an actual rank, it is something added to your rank. In order to be eligible for rewards on signature bounties, you have to be minimum Jr. Member." - from a bounty manager.
That's up to the campaign manager. In
my last campaign, I accepted Copper Members of any rank. The catch is of course that they also needed to have
earned 35 Merit.
Anybody with such high post quality, including Newbie, is welcome in any campaign I run.