So let me say this about UMG and Slate, UMG is UObject-compatible frontend of Slate, created to make Slate usable in blueprints (as all Slate classes are non-UObject and invisible to reflection system there for can’t be used in blueprints) and all UMG widgets (with prefix U) are containers for Slate widgets (with S prefix). So slate practiclly have same widgets… even more widgets them UMG has
To get underling SWidget of UMG widget you use this function:
Also alternatively you can easily construct Slate widgets, it really super easy which makes Slate very easy to use in C++, here examples:
But i understand you want to use UMG editor to declere Slate widgets insted ;]