No question, there are quite few people who pump their reputation by upvoting for their questions/answers using different accounts. I don't think it's the appropriate behavior. Do you?
This is, of course, not allowed on any of our sites. This is not a matter of individual site policy.
Moderators are equipped with tools to detect invalid votes (both up and down) and any such activity is gonna result in a suspension.
Now, that's assuming you're speaking hypothetically. If not and if you have suspicions about specific users, please flag their posts for moderator attention, leave us a note and we'll investigate.