They are generic -- no personalization, can be used by anyone.
Be aware though -- Southwest's system limits the number of forms of payment that can be used on a single booking to three. So someone wanting to use, say, 4 or 5 $25 gift cards for one flight won't be able to. And there's no way to combine separate cards, or add more value to one. Also, once they are used, if you cancel that flight, the refund won't be back to the gift card -- it will be in travel funds, locked to the name of the original passenger and valid for one year from the booking date.