ok first of all keep the irs out of this because they dont care if your legal or not... all they want is their money...

the military will not let you join if your illegal period! they know that by letting someone join that is not legal is a road to citizenship and they are not going to make it easy.

the two cases you listed are unique... they beat the system somehow... but that doesnt mean you can just walk in a marine corps office and sign up... try it just kicks lol they will turn you away. Sure they want you... they just cant...

the bottom line is as long as your still undocumented its not going to happen...