I think you are pobably right. I was thinking about creating a character that uses a lot of summoning; summon demon for close in melee fighting and summon undead for ranged magical attacks. I was hoping I could get a bonus as well. There is a skill that increases the damage of your summoned creatures. I only have summon ghost which is a life saver. I don't think the summon mastery skill helps them though. Not really sure because from time to time my ghost does seem to attack.
