Ahhh, think I figured it out, it should be:
public voidAddUserToContactList(stringuserLogginID) //Add parameter user logged in user's contact list
{
ChatSystem.Instance.GetCurrentPortal().DataManager.AddContact(GetLoggedInUserIdentity(), "User:" + userLogginID);
}
This seems to add the user approprately. Still integrating the other answers and they work great. Thanks for your help!