Seed traces in seedless grapes are almost always unviable.
Us grape growers propagate these vines from clones. Breeders who work with seedless grapes have some horomonal techniques that can get a vine to produce some % of potentially viable seeds. Or one parent in the cross is a seeded variety and the seedless grape is just the pollen source.
There won't be any viable dormant hardwood with buds on a cluster like this in the grocery store. You'd need to do tissue culture. Which involves labratory equipment, a pile of chemicals, and a totally sterile environment.
Maybe it’s harder for plants, but people do cell cultures at home and cultivate them into “fruits” all the time in mycology. Including plates, filtered laminar(ish) air flow and sterilization.
Dealing with plant cells seems a lot easier because you don’t have to conmpete with spores floating all around.
You could buy a certified clean room that’s inspected for $20k. Or build your own for a few hundred bucks.
Second, if they didn't, that would be entirely pointless.