Can I use free vectors with standard license in a book?

The free assets come with a standard licence and can be used accordingly. I recommend studying the licensing terms and see if your use applies. If the main value is not the stock asset, I would say yes, go ahead.

Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).