It is Las Vegans (pronounced VAY-gans).
I think the vast majority of the fanbase are people who live in the areas. Yeah you have visitors and people seeing games that way, but being the first major professional franchise galvanized the area to the fandom and became the primary team of the people who live there. Vegas, just like Denver, is a heavily transplant city... just they didn't have something already there, they gained from it it and galvanized. Whereas the Avs have been around for a long time now and people moving from Chicago just tend to stay Chicago fans.