Voting bots are not against Steemit rules as of now. There are no written rules. Steemit operates as the Steem blockchain code asks it to. Steem witnesses have huge impact on how Steemit functions.

There are some risks due to fluctuating prices of Steem and SBD. It can be profitable as well as disastrous to get a vote from a bot against a payment. If price rises after the vote, you profit and vice versa.