You got wrong assumption.

You can not use different accounts in the same bounty or signature campaign if the bounty manager strictly have this in his rules otherwise you are okay with multi accounts.

So the forum management and none of the members are not stopping you to have more than one accounts.

Rules are here: https://bitcointalk.org/index.php?topic=703657.0
And I did not find anything about not joining in the same campaign yet.