Funnily enough, the photo in your signature has a unit with sand hoses at the rear of the front trucks and the front of the rear truck.
Remember, a unit isn't always facing "forward". If the sand hoses were both in the "front" of the truck, then whenever that unit was going long-hood forward (or just backing up), both sand hoses would be facing the wrong direction.
Having a set on either end of the front/back ensures that, no matter which direction the unit is a facing, there's always sand being applied in the correct direction.
I can't speak for whether some railroad ever just put the hoses both on the front of each truck (though it would seem odd to me), but I can say that it's not unheard of for them to be at the rear of the front truck and the front of the rear truck (so the hoses are both facing the fuel tank). More commonly, other railroads have ordered them with the hoses opposite of this, so they're both facing outboard. And most commonly they'll be on both ends of both trucks. In modern times, most everything ordered past the GE Dash-7 and the EMD SD45 have had sand hoses on both sides of both trucks -- I guess it's possible to get just a single hose on each (you can order whatever you want), but I always see hoses on both sides. For GP38-2s in particular, I've seen them with hoses on both ends of both trucks, and I've seen them on the outboard side of each truck, can't say I've ever seen them on just the inboard sides and definitely not on just the 'front' of each.
