You do, and Yuffie is necessary if you want to get all the summons/Master Summon materia.
If you're not worried about that, then it's just Vincent. In fact, you don't actually have to get Vincent. You just have to beat the boss that allows you to go find Vincent in the basement.
Still been playing Alpha Sapphire. I'm like 90 something hours in and I'm the League Champion. I'm finishing Delta Episode to get Rayquaza and then filling out the rest of the Hoenn Pokedex before I probably call it quits. I might fuck around in the Johto region to grind levels for the Pokemon I need to evolve.