Most online casinos will permit you to play scratch cards with a no deposit bonus. Please check out the terms and conditions for the bonus to make sure that you can play them. If you cannot find any mention of scratch cards as a restricted game, then it would be best to contact the casino support directly to inquire. In most cases, they will let you play scratch cards with a free bonus, because the odds are similar to slots.
Some of the online casinos fail to mention scratch cards when it comes to their no deposit bonuses, because they aren't as popular as slots or other games within the casino. Not all of the online casinos offer scratch cards. Many of the casinos that cator to US players have very few scratch cards or none at all, while some of the UK casinos have scratch cards that are branded after Monty Python and other movie themes.