I think HP knows, that is why people can be penalized for malicious behavior. Also, each time you vote, there is a note from HP that acknowledges your vote.The recipient of the vote does not know. But one should remember that we are all writers and if the hub does not deserve the vote(either up or down) you gave it then you are dishonest.
I am not sure if Hp knows who rates the recipes though. In any case voters should be true to themselves and vote honestly.