I had just now come across a suggestion to post Deep Dream generated stuff as NFT's. That may be OK, as long as both the original image and the deep style used is your own. But most that use Deep Dream are using styles from others, or styles from the program. On the Deep Dream website, sort of hidden unless you open the subscription page, there it says the following:
Do I own the processed images?
Yes, you do. But if you plan to use the result images commercially, you have to make sure you own the rights on the input images (and style images in case of the Deep Style tool).
Myself, I had used my own styles often, but also used other styles that are on the system. So one has to be careful to be within the legal rights to commercialize ones stuff.