I might as well set up my defenses, as well. Before entering the cave, I cast my extended Mage Armor, Polymorph, and Greater Magic Weapon after the Polymorph. I take 10 on Knowledge (the Planes) to know about Dwarven Ancestors, MM4, exceed the check DC by 8 (5 HD outsider = DC 15). Before casting Polymorph, I take out my granite statue and place it on the floor, then use the command word to make it grow to large size. I cast Polymorph, and assume the Dwarven Ancestor's form. My Otherwordly feat makes me an outsider, thus I can assume the form of an Outsider using both Polymorph and Alter Self. My spirit as a dwarven ancestor inhabits the now Large sized statue. I am now Large, with a +18 Natural Armor bonus and DR 10/adamantine. My total AC is 30 (the ancestor is large and has 8 dexterity, so -1 dex, -1 size, +18 natural armor, and +4 armor from Mage Armor). I cast Greater Magic Weapon on the greataxe I hold, giving it a +2 bonus. I also gain a +7 to my fortitude save, because the Ancestor has a 28 constitution and I can still wear my +2 constitution necklace.
My attack bonus is:
3 Base + 6 Strength + 2 Enhancement Bonus - 1 Size = +10
My fortitude save is now +14
My reflex save is now +3
My Initiative is now +15
AC: 30
DR 10/adamantine
My damage rolls are 3d6 (Large Greataxe) + 6 (Strength) + 2 (Enhancement Bonus) = 3d6 + 8/x3
My Speed is 20 feet
My reach is 10 feet
I retain all my spellcasting abilities
Have I won, yet?

Keep in mind, that, actually, just ONE of these snakes is meant to be an at-level encounter. Also, regarding the "flee if they don't die in the first round," the basis of victory was explicitly stated that once my victory is inevitable, the encounter is over. I could fight tons of these things and not break a sweat, they can only hit me on a 20, they can't deal damage except on a roll of 6 and thus cannot inflict poison (I must be injured to even save) and even if they could poison me, I pass my fortitude save on a 2.
I would also argue that, as an animal with an INT score of only 1, even a viper lookout would continually try to attack until it died. I'd, in fact, argue that vipers are not intelligent enough to have "lookouts."