First of all it is not a very common used pattern, while people using it do their best efforts to spread its usage.
Unreal like Unity is a EC (notice missing the “S”) Entity-Component based Game Engine, the difference with the well-known ECS pattern is that logic is still present in components in UE4, I think it is actually possible use a full ECS approach with UE4 (even if not natively supported), the main problem would be for networked code, for which at some point you’ll need to pass from an Actor, but apart that you can threat certain Actors as components (pure data) and certain actors as systems (pure logic) without too much issues in UE4. However be aware that I saw no major experimentations with UE4 and ECS pattern so there could be some subtle issue that you will it along the way if you decide to do ECS with UE4.