There are a lot of dummy accounts on steemit like aizen01, aizen02, aizen03, aizen04 ...
The aizen accounts, as well as most of the numbered "dummy accounts" like the badgers, are miners... (you can see them finding POW on the steemd link). you have to create multiple different accounts to mine, because your miner has to "sit out" while its waiting for a witness.
So theyre dummies in a way, but most of them arent sybil armies or anything.. needing to create them is just part of how mining works.