You can be sure that the Obama campaign and SuperPAC will tailor ads in Ohio to tie Romney (or any GOP nominee) to Kasich and SB5.
Even when someone isn't on the ballot, they can be part of the campaign. Just ask Bob Dole who was tied to the very unpopular Newt Gingrich (with ads talking about the "Dole Gingrich Congress"). Or ask Newt Gingrich who has to explain why he is on a couch with Nancy Pelosi.
Agreed. Any high-profile Republican with a personal scandal, proved extremism, or general incompetence within a State can only hurt the Republicans. "Just like John Kasich" is a good way to go after Republicans in Ohio. You can say much the same of Walker in Wisconsin or Scott in Florida.
That's not to say that such a rule doesn't apply to Democrats, too.