will this irule work?

I think this rule should work, though I'd make a couple tweaks.

when HTTP_REQUEST { 
    switch -glob -- [string tolower [HTTP::uri]] {
        "*/admin*"} {
             HTTP::host should be fine as long as you're using the default port. If you use a different port than default, you'll need to parse the host.
             If you know you're already on HTTPS, you could just use "/someother/index" too
            HTTP::redirect "https://[HTTP::host]/someother/index" 
            return                
        } 
        "*/someother/index*" {
            pool MY-ADMIN-POOL 
        }
        default {
            pool MY-OTHER-POOL
        }
    }
}