Who are the animators responsible for Madoka Magica?
As senshin answered, the design of the witch mazes was done by Inu Curry, so considering the motivation is about where they might have inspired themselves in, I'm pretty sure that answers you quetion, but for some supplementary info if you want:

http://wiki.puella-magi.net/Madoka_Magica_Staff_and_Cast#SHAFT

It has all the entire animation staff that handled Madoka Magica, including which episodes certain animator directors were responsible for, etc..