Unity's DOTS is definitely an ECS system. You technically can have an ECS without all the data-oriented and cache efficient stuff, if you just want the architectural benefits, but it's pretty hard to build a data oriented game engine that is not fundamentally ECS
Definitely true, having looked at probably 20-30 ECS frameworks in about 5~ different languages between 2019 and 2020. About half of the ones I looked at, probably a bit less, were DOTS.