Can spectrum be underslung on Dana Dolly?

Yup, spectrum ST4 can be underslung on the Dana Dolly. For this to be successful, the moving pan axis needs to clear the bottom of the rails and belt. Therefore, you will need a ball head or a riser to lower the spectrum far enough and keep it out of the way (seen in the image below).  The picture above was using a:

• 500BALLSH - Ball Adapter, inverted, clamping down the 100mm ball receiver included with most Dana Dolly Kits.  
• BH-55 Ball Head RRS - with a Screw Knob Arca Clamp that interfaced directly with the Arca Compatible 50mm plate mounted to the bottom of the eMotimo Spectrum ST4.

In this configuration the Ball Head added another 3.5 inches from the base of the 500BallSH to the ST4's mounting plate and offered plenty of clearance between the bottom rails and the bottom of the spectrum.

Tips!- the screen of eMotimo can be inverted in the settings menu to make programming easier.  Additionally, any of the axes can be reversed in the eMotimo settings menu so your controller input makes sense to you!  

Safety first - ALWAYS add safety to the camera in this configuration.  When initially mounting, always load up and test for double or tripled the weight of your payload before letting go.