Maybe if its something like a Cowboys fan or a Bears fan, but not if its a Niners fan or a Rams fan. Seahawks too have a long rivalry, many of their fans aren't going to be fond of the Raiders. Now all the other AFC West fans, which has to be at least 30-40 of Vegas since the Broncos, Chargers and Chiefs are big in these parts, and fans of popular AFC teams like the Steelers and Pats aren't going to be willing to take a second team in the Raiders. Frankly, I think this second team concept will only work for the not so serious fans, who are basically what the Raiders have attracted so far. People that say something like "I like football" and then are happy the Raiders are around, but die hard NFL fans are nothing like that.
What you will see is what everyone has been mentioning, which works great for Vegas when fans are allowed, having people drive in from So Cal and other parts of California to support the team along with the Raiders fans who already lived in Vegas or have moved in during recent years. The model works for the NFL, but no other sport. Teams like the Packers, the Chiefs, the Broncos, the Niners...all get fans to drive multiple hours each way to attend games.