In the sixth episode of the show, we found out about Shady Sands’ fall in 2277. Four years before New Vegas starts. This retcons New Vegas. No one in the NCR talks about how their capital got nuked in NV. In the quest You’ll Know It When It Happens, the president of the New California Republic visits the Hoover Dam. Why would the president visit the dam after the capital got attacked? Hell, why is the NCR still in the Mojave Wasteland? It doesn’t make sense. So yes the show does retcons New Vegas.