I'm not really sure of all the specifics of how witnesses work, but what I know is that the witnesses run various nodes that make up hive's server. Then whenever there is an improvement that has to be made they create proposals which we vote for . Then whenever a certain number of votes is reached the funds to implement are released from the decentralized hive fund.

Also they get rewarded in hive for running the witness nodes.

Seems I need to do some more research on what hive witnesses are?

Oh yes, and I've voted for a couple witnesses who I happen to come across their proposal.

!1UP