It -is- possible to enter the minefield via the opening in the mines, however, you should not do it unless you are LSF or LN.
Missions are decidedly odd in what they wish you to do/go...I have had a "destroy installation" mission with the waypoint on Buffalo (LN mission), as well as a RM mission, again "destroy installation", asking me to blow up the new Unioner base in Hamburg.
It would be nice, however, if the missions in Alaska, at least, could be removed...