Yes it can. It simply means the subclass implementation has no access to a this pointer. When would undefined behaviour occur here? When a function tries to use a parameter that does not exist in the function signature, that's a compile time error not UB.
Maybe you think that, because a this pointer is needed for dynamic dispatch? A this pointer exists there, it is just not passed to the implementation.
Maybe you think that, because a this pointer is needed for dynamic dispatch? A this pointer exists there, it is just not passed to the implementation.