Hi! I don’t think direct import is possible currently. But you can download images from Adobe Stock and add them to the image placeholders on the new Adobe Captivate project slides. Adobe Captivate also has a large collection of images, characters, and icons available within the tool. You may explore them under the “Asset Library” on the left navigation panel.  

AFAIK the answer is negative if you mean ‘are they for free’. Amongst the free assets in Captivate some are from the Stock but that was already the case for version 11.5. If you want to use more Stock assets, you need to buy them.