Google will still scan your mails but you will not be shown any ads.
For viruses and spam, yes. But Fastmail does that too.
In addition to these increased security measures, as we recently announced, we’ve now turned off ads in Google Apps services. This means administrators no longer have the option or ability to turn on ads in these services. We’ve also permanently removed all ads scanning in Gmail for Google Apps, which means Google does not collect or use data in Google Apps services for advertising purposes.
I agree that Gmail (especially via Google Apps for Business) is a great mail provider. My main beef with Gmail is the sub-par IMAP support.