Only fedded countries can get help from each other with helli and ints. There is nothing stopping you making your own fed for just your main and your slave.
Here's my view on this: if I want to defend a city with nothing but two NDB, then I should be allowed to do so.
My reasoning behind this is simple. They're MY weapons. I should be able to put them wherever the hell I want to in my own country. If I want to defend a city with nothing but two NDB, then why not? They're MY weapons, and it's MY city!
It can also attack a C3 remaining secured. Hmm, not sure how that works on the higher war levels when the C3 can fight back, have I just found a loop hole?