SHAREPOINT Crawler Traffic Segragation

Your code looks correct. What indication are you getting that it's not working? Try adding some logging:

when HTTP_REQUEST { 
    set uagent [string tolower [HTTP::header User-Agent]] 
    log local0. "incoming uagent = $uagent"

    if { $uagent contains "ms search"} { 
        log local0. "found a robot"
        pool pool_crawler 
    } else { 
        log local0. "not a robot"
        pool pool-NonCrwaler 
    } 
}