They definitely do, and if my memory serves me right, they disappear right away.

Ment, with all due respect to your experience in Heroes 5, but your memory is failing you here. I just checked, created two duel heroes, Dyrael and Vlad. I gave Dyrael the Summon Elementals, Fire Warriors, and Elemental Equilibrium skills, and limited Vlad to only Summon Elementals. The result of the experiment: Dyrael summoned Fire Warriors, and Vlad summoned Air Elementals, and immediately, the same number of Stone Elementals appeared on Dyrael's side, while the Fire Warriors did not disappear.