There’s plenty of GOP voters who would not show up if a black man was on the ticket
citation needed
How about the countless Conferedate sympathizers?
I find it unlikely that there are large numbers of people who wouldn't show up if a Black man is on the ticket. Tim Scott has already participated in elections in South Carolina as a black man and did not lose much support compared to other Reoublican candidates.
In fact, it seems he's done a good bit better (especially in 2016, after South Carolinians knew his race for two years, Tim Scott got nearly 100K more votes than Trump while his opponent got nearly 100K less votes than Clinton).
Will these people who take issue with Scott's racial background suddenly start coming out of the woodwork in the rare scenario in which he is nominated? Where would they come from? It's not South Carolina, that's for sure.
Also look at 2014, when Scott outperformed the very white Lindsey Graham by several points despite the former being an appointee who'd never run statewide and the latter being a two-term incumbent.