Naw it can only damage you. Companions, summons, etc are all immune to your fireball.
Its still SUPER fucking annoying every time I tried to fireball a troll only to have it change targets and rush me as I hit the spell - position is key. So many suicides and reloads before I gave up on fireball and respec'd as a summon/autoattack mage that uses zero spells.
Side note: Outside of a terrible (sorry I love your game though) variety of staffs this build is super fucking strong. This thread makes me want to try more conventional builds but lv 18 iron golem + 35dps auto attacks of the damage type of my choice + 40 armor + knockback/stun armor is incredible. Only problem I've had is the lower floor of the Ark because my summon gets wrecked by the radiation balls.