Hello!
The short answer is that you can use any of the marketplace assets (free, paid, and/or epic content) in most ways that doesn’t include distributing the source files.
So showing marketplace assets in a video (trailer/tutorial) is 100% fine 
More info here: Marketplace FAQ
How can I use the products I’ve purchased from the Marketplace or Learn Tab?
Besides using them for learning, experimenting, or prototyping, you may use Marketplace products in your own shipped products. However, you can’t sell or sublicense Marketplace content to other developers for use in their products, e.g. via website or ecommerce mechanism built into a 3D development tool.
Cheers!
Joakim