There's no doubt that Meade's supply lines were vulnerable and this is one battle where the PACS was generally better supplied than the USA; just read the OR for the US officer's complaining about their supplies and how much better the PACS was faring.

That said, CS Cavalry harrassing his supply lines would have given Meade pause, but he had Cavalry too, Cavalry that didn't do badly against the CS, and he had the high ground.

Some Yankees might have gone hungry for a few days and ammunition might have been shorter, but G'burg was fundamentally an infantry battle and I don't see how any cavalry action, once the battle was joined, would have changed much.