No, they use sendmail.
The spammers are hard to trace, they use loads of IP's (probably spoofed) so now we are heavily logging the SMTP connects with thanks to DedicatedNow who is monitoring every move (they hate them even more then i do

)
Anyway we're all on it and when everything is sorted i will write a wiki page that should explain the massive abuse of our and your server to spam the world, since cPanel, Plesk, etc. are just not good enough to block it.