for everybody else having similar troubles, using
using System.Runtime.InteropServices;
and inside your node class:
System.Runtime.InteropServices.DllImport("yourDLL.dll")]
private static extern int yourDLLExportedFunction();
works fine for me. yourDLL.dll needs to be in the same folder as vvvv.exe, or you specify a path instead.
yourDLLExportedFunction is the function of interest, exported by yourDLL.dll; which should be declared in it’s documentation.
after importing it this way i’ve been able to use the functions right away; copy paste edit the lines for additional functions to import.