It's not that grey. It is expressly illegal to pay someone to register to vote and a lottery prize is specifically called out in the statute as a forbidden form of compensation. It is a felony and punishable by up to 5 years in prison.
What CAH is doing is a grey area, paying people to create a voting plan isn't mentioned in the law so it skirts around the legality of it. This should probably also be illegal as a form of voter compensation but may require the law to be amended.
It will also motivate Trump voters to get to the polls to counter. Plus a 2-1 at this point just shows Democrat enthusiasm being high, which is good, but early vote numbers are a poor predictor of election outcomes.