True. Multiple accounts and cross voting from one account to another is common. Though to draw money or shift Steem outta Steemit, just one account (the primary one) is used (my limited observation)

At the same time, people make multiple accounts and keep one of them accounts just for upvoting minnows and plankton (again my limited observation over the last 87 days)

I have myself been beneficiary of receiving massive upvotes from such accounts on 4-5 occasions.