Go easy with it. You have nothing to lose. If you can't rod it, you will have to dig it up and if you tear up the pipe you will also have to dig it up. Try before digging.
I'd try a smaller head first and a root cutter as the last resort. Go slow and you will have to wash the dirt out with a hose and high pressure spray end as you go. There is no telling where you will go when you get to an elbow or tee. Your best bet may be to have a plumber go in with a jet cleaner.
If it is hard packed for very far, it won't be easy. Even if you poke a hole in it, it is already filling up with dirt anyway. If you replace the pipe, get some covered with a filter fabric. Good luck.