Im confused what his plan is supposed to achieve. It sounds like he wants the rangers to save the day when the troopers fail to hold the dam. But how does falsifying intel reports achieve that?

Also, do the choices in this quest (don't turn him in, turn him in) affect the endings?

I thought he wanted to cause chaos with the intel so that NCR might pull out as they shouldn't be in the Mojave as it's only bleeding them dry.

^this. i like the NCR but i think they just need to stay in California.