Of course they can pick out their fires if they bred a known fire to a normal. Then you know exactly what you have. When you see them beside the other babies, especially after their first shed, it's obvious.
Just like I have no problem at all picking out the Russo hets from the normals in my clutches. After you've produced them from proven morphs it's easy to tell. If you know for certain what you're starting with, then you know what you'll end up with. Breeders develop an eye for the subtle morphs. It's no different than a breeder being able to pick their mystics from a clutch. Or their specters.
If you are starting with a "dinker" however, you don't know exactly what you have, therefore you don't know what you'll get. Even if you got babies that looked like the dam, you still couldn't say they were fires until you produced a leucy. All BPs reproduce their selves. Wether they are a morph or not. Color and pattern is passed on. This is why all the time we see people talking about how they bred this dinker to that dinker and they produced babies that looked just like the sire or dam. Ive seen a lot of these where those dinkers looked like regular jungle patterned normals and they were just producing babies with the same cool pattern but nothing more.
The point is, the more a person pushes for a yes answer, the more they be told it must be bred to be proven. All we can do when it comes to possible subtle morphs is give our opinion. Our opinion is what will help you decide the best mate for breeding to ultimately prove if its a morph or not.