Bump means posting for the sole purpose of taking the thread to the top of the index, and it doesn't have to be the OP who is bumping. Hence the comments that try to reduce the practice of necro-bumping. Using alts to conceal the fact that a member is bumping is against the rules of the forum.
Bumping service is not allowed, but bump by OPs is allowed if following two rules above. Accounts which join or give bumping sevice will be nuked, as I know.
Basically, such bump posts don't violate forum rules, if posters follow two following rules.
13. Bumps, "updates" are limited to once per 24 hours.[2]
21. Old bumps should be deleted. [2]