Yes, you certainly can if you want. The Avada Builder is a much more mature and feature rich option, and so the block editor could be seen as a poor choice, but technically there is no limitation to use one or the other. What must be noted though, is that if you create a page/post with Gutenberg, you cannot edit/maintain the same page/post using the Avada Builder and vice versa. They are not interchangeable. Any Gutenberg page/post created though, will display perfectly on the front end of the site to anyone viewing it.
Some people have decided to use Gutenberg on their blog posts for example, for future protection if they ever change WordPress themes. This way they would only need to reconfigure the pages, and not the posts.