Indeed. This is a good reason among others which made me choose Unreal Engine 4 as the 3D engine to create my first game. And thanks to this I know that what I buy on the marketplace I can re-use again and again in future projects with no worries and no fees.
And this too in the faq:
It means that you can use any asset and any code you buy on the marketplace as the starting point for your projects, modify it, improve it if you can and learn from it… use anything as a tutorial to be able to make your own the same way, modify as much as you want everything you use to create your own custom version.