Does the Spell Specialization feat follow the Summon Monster series of spells up the ladder? IE if I get Spell Specialization on Summon Monster II does it apply to SM III, SM IV etc?
Only if you choose to make it do so:
Every time you gain an even level in the spellcasting class you chose your spell from, you can choose a new spell to replace the spell selected with this feat, and that spell becomes your specialized spell.