I need to speak to him inorder to attack Hoover Dam. Im in Legates camp but cant find him anywhere. Also does anyone know how close to the end I am. I accidently ran into a spolier and it told me Legatus ends up as ruler. Is it still worth playing to the end?

If you head right to the end of the camp area, on top of a small bank there is a tent / house.
Look around for the door, as soon as you enter a cut scene happens and he should talk to you.
Then you just follow his orders.