Pointer to uninitialized data member

Is it safe to store reference/pointer on uninitialized data member? Not use, but store at some moment of time.

I know that I have to use smart pointers. But for code simplicity I decide to give an example with owning raw pointers. Which is not very good in practice but I think good enough for example.

Here is the example of code:

struct Node {
    Node(Node*& node_ptr) : list_first_node_ptr{node_ptr} {}

    Node*& list_first_node_ptr;
};

struct List {
    // Is this line - dangerous?
    List() : first_node_ptr{new Node{first_node_ptr}} {}

    Node* first_node_ptr;

    ~List() {delete first_node_ptr;}
};

I initialize first_node_ptr with Node object, but pass in constructor of Node object still not uninitialized first_node_ptr.

One more question: is memory already allocated for first_node_ptr when I pass it, so will the reference address at Node constructor be valid?

I think that this example is about the same but simplified version. I'm right?

class Base {
 public:
    // var_ptr points to uninitialized va
    Base() : var_ptr{&var}, var{10} {}

    int* var_ptr;
    int var;
};

P.S. Why when I write (Node*)& instead of Node*& I get compilation errors about incomplete type?

P.P.S. Can the usage of smart pointers change the situation?