A lot of answers are in the ultimate manual.
http://forum.1cpublishing.eu/showthread.php?t=18453
Something gets lost in the translation, but basically the summoner skill affects these abilities.
"""Operates on spells Natural Call, Necromancer’s Call, Portal of Demons, Phantom and on talents of beings
Give birth Gobots, Heavenly Guards, Appeal of Demons, Demonic Creatures, to Call Thorns, to Call the
Bear, to Lift Undead, Budding and Sowing.
"""
Rune Mages are not listed though since the manual was written before rune mages existed.
Same with the engineers. It is possible they do not consider them in the group, or it is a bug.