What do you mean, mining code of the pool?
Each individual miner has his own code, and they submit shares to the pool - or am I mistaken?
Miners just blindly accept work from the pool.. they would quite happily go to work on mining a block containing a doublespend tx if the pool assigns it.
That could actually be changed if people cared.. the end miners could maintain their own view of the blockchain and refuse to work on anything that goes against it.. however that isn't the current situation.