Can I run two non-thunderbolt displays from a thunderbolt RAID device?
No, not with the Promise Pegasus R4 has only two Thunderbolt ports. One you will need to connect to the MBA and then other to your miniDP adapter. You would need a Thunderbolt dock that has another Thunderbolt port or another video interface like HDMI, etc.

Something like this: http://www.caldigit.com/thunderboltstation/,etc