Combine the water, granulated sugar, and the vanilla bean (add both scraped seeds and pod) in a medium saucepan. Bring to a simmer over medium heat, stirring until the sugar dissolves, 2–3 minutes.
Add the peaches to the vanilla syrup. Adjust heat to maintain a gentle simmer and poach, turning once, until a knife tip meets slight resistance at the center, 5–8 minutes depending on ripeness.
Remove the pan from heat and let the peaches cool in the syrup until just warm, 20–30 minutes. Lift out the peaches to a board, slip off and discard the skins, then halve and remove the pits. Return the peach halves to the syrup, cover, and chill until cold, at least 1 hour.
To serve, place scoops of vanilla ice cream in four chilled bowls. Nestle two peach halves per serving around the ice cream and spoon the chilled raspberry sauce generously over the top. Serve immediately while the peaches are cold and the ice cream is firm.