Blueprints are not similar to C++ function… Blueprint functions ARE C++ functions (except some custom flow nodes) and C++ API reference already mark functions and variables available in blueprint with blue file icon
https://docs.unrealengine.com/latest/INT/API/RuntimeModules/Engine/GameFramework/AActor/index.html
Engine automaticly generates nodes that are flaged
UFUNCTION(BlueprintCallable, Category="Input")
virtual void DisableInput
(
class APlayerController * PlayerController
)
Arguments become inputs (or else HidePin is used) return type becomes return value output, it takes name of a function and adds spaces automaticly (or else FriendlyName or DisplayName meta i used).
So yes you can use C++ API refrence as a Blueprint API reference already I think they could add blueprint filter in API efrence so you can only see stuff available for blueprint and some specific icons from blueprint callbale, blueprint pure etc.