IW4MADMIN doesn't work on Zombies
It doesn't connect to IW4M and apparently its a limitation on Pluto's end
These same settings work on MP
I've tried IW4Madmin on WAW Zombies too and it simply just does not work for me. Maybe something will happen in the future to fix it though.
rcon in general doesn't seem to work in zombies (i've tried useing multi rcon as well), nor does logging work, so there isn't a way to use iw4m-admin with it, at least at the moment.