Yes he can. Snares/roots only prevent the enemy from using their movement spells but you are still free to use any knock backs or pulls to move them around.
Unless you're asking if a root will cancel once they're hit by a knock back in which case the answer is no.
I guess my awesome Blitz + Lux bot kill lane idea will work then...
^That bird posts as fast as it flys^
On a side note, when Awwww Yeaaaaahh answers a question on the redtracker, do you hear a voice in your head answer the question as "Awwww Yeaaaaahh"
"Can Blitzcrank pull an enemy out of a snare?"
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