I think in most cases they are not uesd too much in hydroponic
nutrients. Amonium is not readily obsorbed from plants to my understanding and takes enzymes to break down into a useable for for the plants.
Most commercial hydroponic solutions tend to use nitrates rather than other forms. You will usually only find ammonium and ureum in organic hydroponic solutions as they also contain the enzymes that let these things be usable.