OK so while looking at the Fallout 2 endings on the vault wiki i read ending 4 where NCR becomes more Militaristic and how the Enclave join up with them here the ending.
"Shaken by the assassination of Vice-President Carlson, right-wing elements seize control of the Congress and set the New California Republic on the path to military rule. Eventually the survivors of the Enclave find a new home in the ranks of the NCR".

How would NCR be like in 2281 at Vegas?

That ending doesn't happen. The NCR ends up hunting down remaing Enclave and killing them. The Brotherhood does the same. NCR don't become a military state, but it does have a large military.

My hope is Enclave remnants on their way to DC find their way into the ranks of the Midwestern Brotherhood. When the renmants fail in DC they regroup and join in Chicago.

For christs sake, he's not saying "THIS IS HO IT SHOULD BE", he's asking for ideas as to how the NCR would be by the time of New Vegas if things had ended that way in FO2. Do hypothetical questions go right over your head?

As for how they'd be in FNV, I doubt the Legion would even be a problem, and House wouldn't even have a chance to get uppity once he showed even a barest glimpse of his hand. The NCR would simply kill, steamroll and crush anyone and anything even pretending to pick a fight with it. The Legion would be hunted down to a man before even the first battle of Hoover Dam, House would be killed very early on, and the BoS wouldn't have survived Helios One.

Wouldn't the NCR be Authoritarian also.

They would not have much of problem with the Legion, as the Legion would have nothing to counter aircraft, power armor and likely some tanks that a NCR with Enclave technology would have have. The BOS if they exist would have nothing the NCR does not have, as the Enclave Member would likely get started on making new power armor. House would likely just fall in line and join the NCR.

Life in NCR would not be that bad those, as robots would likely deal with heavy labor and the technology would be high.

Well it gives very little info about the Enclave, for all we know the enclave just wasn't hunted by NCR and eventually found their way into the NCR's military, which is what I would expect, not the Enclave willfully joining them.

So I would expect that the technology would be relatively the same, there were just be more troops, more rangers, and they would all potentially be better trained. Due to this the Legion known as it is would probally just be crushed by the NCR, but the Legion is smarter than that and probally wouldn't of just waged war on such a powerful enemy. If they wanted the dam they would take a much more "sneaky" approach than just capturing places in the Mojave.