Yes, it's just a size thing. There's no reason not to feed them when they are small.
The reason most people avoid them as feeder insects is because roaches generally have a long life cycle (for a feeder insect): by the time they get too big to feed off, they're still young enough to be around for a long time still. And if you've got a successful breeding programme going, you might end up having to keep alive a lot of useless adults which means a lot of feeding simply for the sake of keeping them alive (unless you plan on euthanasia as an exit strategy).
But if you simply have excess small roaches, then gutload them properly and feed them off to your chams...