Actually, that is not true. The Sidar have Spirit, Enchantment, and Body, none of which have summons.
That is one reason why several posters have suggested giving them Shadow Mana. I was strongly against the idea at first. For one, their UU already has shadow magic, so ti would be less useful for them than for other civs. Also, the first poster recommended giving shadow in the place of spirit, which I consider this their most important and thematic sphere because they were founded by the use of Laroth's spirit magic. When they recomended replacing Enchantment I was also against it, since Laroth's ability to bind spirits to weapons (like the netherblade) thus enchanting them made me think that the Books of Laroth that the Sidar still posses probably contain lots of knowledge on enchantment as well. Originally I was opposed to replacing Body with Shadow because the act of becoming a shade is done specifically to preserve the body and make one live forever and since they miss physical pleasures like taste more than deeper feelings like love, but I think I've been convinced otherwise; the Body sphere (and especially Aeron) represent the properties of physical pleasures, lusts, and rage, all of which Shades loose over time as a result of eating away at their own souls. I think I'll probably replace their Body sphere with Shadow in my modmod.