Summoning has always been its own school of spells under the Arcane tree in Shattered Empire. As I’m moving forward into SE 2nd Edition, one of the major spellbook changes I’ve made is to eliminate this school. The individual summoning spells will still exist, they will simply be absorbed by the other schools that make sense to govern the type of creature being summoned. Summoning Undead will all fall under the Necromancy school, Summon Ice Golem will be under the Elemental Ice school, etc. Summoning animals will be under Nature spells in the Spirit tree. You get the idea.
So you can still be a wizard that focuses on summoning, but your Class Points will have to line up with the kinds of creatures you want to summon.