In game, there are 2 summons: the void imp and void woken, which can both fight. Though, they aren't specifically for combat. However, though it's not a summon, you can convert an Ancient into and Archenthrall, which is an overpowered Ancient that is very good at fighting. More summons on the way!
Originally posted by Sleipnir: There is a resurrect job to raise the dead, but I do want to add skeleton summons, or more of a necromantic ability soon.