He's not paying people to vote. He's paying people to register to vote.
It appears to be lawyered loopholes around paying people to register to vote directly. Which is illegal as you mentioned.
Sure plenty of people will sign it for the money and then forget about it, but some sliver of people that sign will feel some sliver of obligation to vote for the candidate that the petition obviously wants them to vote for. A sliver here and there could be enough to turn this currently close election.