For the transport of data between SFDC and storage location, the Salesforce Partner API uses SSL and is approved by Salesforce.com. We are a certified product, and have been since 2005. There are many DBMS’s that offer SSL SQL connections.
For data at rest, if you chose the on-premise deployment, the database security is up to you. In our Cloud offering, the back end database is the encrypted Enterprise version of SQL Server on a server with no public access in an IBM data center. You do not have any access to even your own data in our Cloud offering.
As far as the auditability of security, if you use the on-premise deployment, you own the security. You can lock down your server so you have to log in to the server to access even the web user interface. If you use our Cloud deployment option, you have no access to anything. Recovery is done via a webinar in consultative mode where our professional services team does the actual recovery.