If you want to accomplish anything in Unreal through code, then you have to use some object-oriented features. The way you implement game mechanics is by creating C++ classes which inherit from the standard classes provided by the engine and override virtual methods with your own code. And any of the engine features you want to access in your code are also accessed through objects. So you can not really use Unreal using only C features. You need a basic understanding of classes, objects and inheritance.
That being said, you don’t really need to understand that much about the finer intricacies of C++ to make use of Unreal. The engine API handles a lot of the nitty gritty details of the C++ language for you. Also, the Unreal engine got a very powerful visual scripting system (called “Blueprints”) which allows you to implement most game mechanics without writing any code at all. There are Unreal Engine games which use visual scripting for everything and do not contain a single line of code. Not that this is always a good idea, but it is certainly possible.