[Joeboy]

Blender 2016 DemoReel: https://www.youtube.com/watch?v=mIiY6aGefvI

(Strictly speaking it's a Cycles showreel but presumably everything there will have been created in Blender as Cycles is Blender's rendering engine).

[ZenoArrow]

I couldn't comment on that particular showreel, but it's clearly possible for Blender to use other rendering engines. For example, the linked Miyazaki tribute used Octane.

[Joeboy]

It is, and in fact the default rendering engine is still the "Blender internal" engine. But it's not common to use Cycles without Blender.