Network type access via F5

Right. So it won't work the same - as you say using an Explorer share is not going to use http. I would define a pathname they can use ie http://mysite.com/admin/host.html, then your iRule would look like this;-

when LB_SELECTED {
    if {[HTTP::path] eq "/admin/host.html"} {
        HTTP::respond 200 content "[LB::server]"
        return
    }
}

So they will have the same effect (determining which server is being used) via a different method - note this will only work if you are using persistence and http/oneconnect profiles.