I haven't checked the code, but certainly they appear to be spells and use the new spellbook system. Also, they are subject to arcane spell failure in the normal way. It is true that DNs gain spells like clerics, in that they learn all the spells available for a level upon reaching that level. Otherwise, the DN seems to act like an arcane caster in every way, so I would assume spell focus would work for a DN.
