Looks like in Pathfinder, only the caster summoning the monster can dismiss it. The one who casts Control Summon Monster can only dismiss their control over it.
(Disclaimer: This will only look at the two summoning spells listed in the question. For all other summon spells, please look at the description for that particular spell).
So for the two summon spells of Summon Monster and Summon Nature's Ally, you're looking for the subtle (D) in the duration. If that D is there, then it can be dismissed at will by the caster. The duration for both of these spells are "1 Round / Level". So only the one who casted the summon spell can dismiss them, otherwise they last for the full duration, determined by the level of the caster.
Meanwhile, with Control Summoned Monster, there is no mention of being able to dismiss the monster. In this spell, it does describe that the original summoner can perform an Arcana check to try to win back control. If the check succeeds, then the Control Summoned Monster spell is removed, and would have to be recast to try again. In the meantime, that spell also has a (D) in its duration description, so that spell can be dismissed. But that spell only pertains to the control of a summoned creature.
Also, they would have to worry about controlling a stronger spellcaster's summoned creature. Because the duration of their Control Summoned Monster spell may not last as long as the Summoned Monster spell, and may wear off before the monster disappears on its own!
Lastly, since the general rule of dismissing the spell is there in the duration for the summoning spell, the caster has the ability to dismiss it at any time. This also means even when that summon is controlled by another caster, because the text of the Control spell does not specify that it has the ability to prevent this.
So good news! The thief spellcaster cannot just steal your summoned monsters only to dismiss them. They would need something like a Dispel Magic spell to do something like that. Sure you can dismiss it if someone does steal it, but give an Arcana check or two a try before you do.