F5 Issue with different ports

The primary reason why it isn't working is because the browser is attempting to contact the service on port 8100, which you likely do not have a VIP for. You could technically open up the existing VIP to multiple ports, but probably the better bet is to proxy the traffic based on the URI. So for instance, if the URI for the iView always starts with "/sap", you could send the traffic to a different pool based on that request. Something like this:

when CLIENT_ACCEPTED {
    set default_pool [LB::server pool]
}
when HTTP_REQUEST {
    if { [string tolower [HTTP::uri]] starts_with "/sap" } {
        pool iview_pool
        HTTP::header replace Host "hostname.domain.com:8100"
    } else {
        pool $default_pool
    }
}

where iview_pool is a pool of servers listening on port 8100. Now you still may run into issues if the portal sends references to the iView using the original :8100 designation, for which you may need to resolve internally, or use a STREAM profile in an iRule to replace this with an externally accessible value.