That may be the way it is supposed to work, but I'd still be tempted to enter non-lambic fruited classic sour styles (BWeisse, etc) as Wild Specialty, especially in smaller/local competitions. I've had good success with my Tart Cherry Flanders Red in Wild Specialty, and suspect that if I entered it in as Fruit Beer, I'd get dinged for being sour, or not having enough prominent fruit character.
To me, this may be a difference in theory vs practice.
I'll point out that Russian River Supplication is listed as a classic example of Wild Specialty Beer. This beer isn't terribly far off from a Flanders Red aged in Pinot Barrels (as opposed to fouders) and Tart Cherries.