As far as I know, the object limit in SP is 511. Each generator takes up two entries in the object array (one for the generator and one for the object it spawns). You can unload objects from the array by getting far enough (there's a 64*64 tile square of "active memory" surrounding the player, and any objects outside that area will be unloaded), so separating the areas from each other with thick enough walls might let you use more objects.