First, how can you prove that these accounts were owned by a single person?
These both users have been already tagged by yahoo in attempting to enroll his signature campaign manage.
Probably that was a strong evidence that abusing campaign in a single person joining one campaign that makes them tagged.
Creating alternative accounts is not prohibited by the forum rules but shouldn't use for cheating.
Correct!
@ OP, I think they had already punished by tagging I didn't see any reason to punish them in a ban evasion.
Next time please report with correct evidence and further information that makes them punish.