Well, not all wrong, however the usage of ison is incorrect. You would use that to see if a person was on a specific channel.
Also, there's no need for the if statement, in relation to using the /ruser command. If you use /ruser and the nick isn't there, then nothing happens. Presuming you want that comparison so that the Not on my userlist message comes up, use this.
on 1000:text:`deluser*:#:{
if $ulist($address($2,3)) {
.ruser $2 3
.msg $chan $nick deleted $2 from my user list
}
else {
.msg $chan $2 is not on my user list
}
}
