Is it possible to monitor and gather statistics in realtime (CPU, memory, HDD, network, ... - something like dstat) of guest systems with libvirt through console from host system (KVM based)? If yes, do those guests need to be created through libvirt?
virt-manager has some of this built in, but if you want more detail, look at nagios-virt. Alternatively, you can monitor it by installing the same tools (nagios, ZenOSS, etc) on the guest that you'd use on a non-vm system.
I run munin on my virtual clients to gather this kind of information. Information is gathered every 5 minutes and available in graphical format via rrd. Data is available via http from my munin server.
You can use collectd with libvirt plugin https://collectd.org/wiki/index.php/Plugin%3alibvirt