HTTP monitoring on different port

You can certainly do this. Your monitor would look something like this (replace 10.10.10.10 with your server IP address and put the correct host in the GET send string):

ltm monitor http http-test {
    defaults-from http
    destination 10.10.10.10:5100
    interval 5
    recv "200 OK"
    send "GET /f5monitor.html HTTP/1.1\\r\\nHost: host.domain.com\\r\\nConnection: Close\\r\\n"
    time-until-up 0
    timeout 16
}