As I read it, you are buying tickets to enter the fan zone, not to spectate on the rally. As it does not state that the fan zones are the only places you can go, I would assume that it is possible to spectate anywhere - that is what I am doing anyway.

Obviously as its a closed road rally, most of the land to either side of the road is private, so its just a case of not standing or parking somewhere that will cause PR issues.

The other thing to consider is that if not using the official zones, will probably have to get to the stage pretty early to get in position before road closures.