In short, yes!
We have tested with up to 6 players with a single deck and while it "works" you tend to run out of cards pretty quickly which means a lot of shuffling, and it's a little unbalanced with 5 or 6 players (which is the main reason it's labeled 2-4 players).
Putting two decks together keeps the game balanced and works well up to 8 players, but it does tend to be longer game. With up to 7 other players between turns, there is a lot more chance for people to steal cards or otherwise kill your winning hand. If you don't mind it stretching a bit longer though, two decks work great to get more people around the table!