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I do not know if any other creatures summonable with Summon Monster spells have sneak attack, but the Summon Monster III alternate creature table has Human Natural Wererat Rogue 2 available.
Would that creature get a sneak attack as it appears adjacent to an enemy?
The easiest way the Rogue would get sneak attack was if you were to summon them in a flanking position.
The Sneak Attack ability of the Rogue states:
The rogue's attack deals extra damage anytime her target would be denied a Dexterity bonus to AC (whether the target actually has a Dexterity bonus or not), or when the rogue flanks her target. This extra damage is 1d6 at 1st level, and increases by 1d6 every two rogue levels thereafter. Should the rogue score a critical hit with a sneak attack, this extra damage is not multiplied. Ranged attacks can count as sneak attacks only if the target is within 30 feet.
Emphasis mine.
Being summoned beside a creature would not necessarily deny the creature its Dexterity bonus, so unless summoned in a flanking position or a method to deny the defender their Dexterity bonus is used, the rogue would not automatically get their sneak attack damage.
It would be reasonable to house rule that summoning the creature directly beside a target who was not aware of what spell was being cast would allow sneak attack on its first attack or possibly even full attack.
