The current code is doing something like this when asked for an IDataObject:

HRESULT CFolderViewImplFolder::GetUIObjectOf(HWND hwnd, UINT cidl, PCUITEMID_CHILD_ARRAY apidl, REFIID riid, UINT rgfReserved, void **ppv)
{
    ....
    if (riid == IID_IDataObject)
    {
        CDataObject* dataObject = new (std::nothrow) CDataObject(this, cidl, apidl);
        return ::SHCreateDataObject(m_pidl, cidl, apidl, dataObject, riid, ppv);
    }
    ...
}

SHCreateDataObject already creates already a full-blown IDataObject with everything needed from the (optional) input PIDL(s), including all Shell formats for items in the Shell namespace (CFSTR_SHELLIDLIST, etc.).

Passing an inner object 1) will probably conflict with what the Shell does and 2) requires a good implementation (I've not checked it).

So you can just replace it like this:

HRESULT CFolderViewImplFolder::GetUIObjectOf(HWND hwnd, UINT cidl, PCUITEMID_CHILD_ARRAY apidl, REFIID riid, UINT rgfReserved, void **ppv)
{
    ....
    if (riid == IID_IDataObject)
    {
        return ::SHCreateDataObject(m_pidl, cidl, apidl, NULL, riid, ppv);
    }
    ...
}

In fact, the IDataObject provided by the Shell is complete (supports SetData method, etc.) so you should never need to implement it yourself, it's more complex than it seems. You can reuse it as a general purpose IDataObject (you can pass nulls and 0 for the 4 first arguments).

PS: the Shell also provides the "reverse" method: SHCreateShellItemArrayFromDataObject that gets a list of Shell items from an IDataObject (if the data object contains the expected clipboard formats).