Acetaldoxime Synthesis: Hydroxylamine vs Hydroxylamine HCl
Hydroxylamine is a low-boiling liquid readily oxidized to explosive nitrogen-oxygen compounds.  It is stored as the hydroxylammonium hydrochloride salt for convenience and safety, since the salts do not oxidize as easily.  Additionally, hydroxylamine itself may explode when heated.

The sodium hydroxide is to render the freebase which then may participate in the reaction.  In principle, the hydroxylammonium bisulphate would work as well.

It is somewhat important that an exact stoichiometry be used for base to hydroxylamine to prevent aldol side-reactions if relevant (which for acetaldehyde, they are).  Additionally, this reaction is reversible in the presence of acid and water, so all the acid must be consumed, since water is a byproduct of the condensation.  Given the explosive nature of hydroxylamine, azeotropic distillation via Dean-Stark trap is not viable for dehydration.  Chemical dehydration may be effective.