Is there any way I can rotate an armor stand?

This video goes into explicit detail about how the armor stands work in minecraft, including how to /summon, edit with /entitydata, create custom poses and static artworks.

For your specific needs (look like it crawling) you can use commands to set the angle of the head (Head), arms (LeftArm and RightArm), body (Body), and legs (LeftLeg and RightLeg).

/entitydata @e[type=minecraft=ArmorStand]{Pose:{Head:[~f,~f,~f]}{RightArm:[~f,~f,~f]}{Body:[~f,~f,~f]}{LeftLeg:[~f,~f,~f]}}

Note: the ~f relates to the 3 degrees of rotation - x, y, and z; from 180 to -180.

For example, if I wanted to tilt the head forward by 20 degrees, I would use the command

/entitydata @e[type=minecraft=ArmorStand]{Pose:{Head:[20f,0f,0f]}}