Can I get this kind of DOF out of the 35mm 1.8 DX???

Your statements are both correct (expect for the "narrower FOV"), as well as the calculation above. The confusing part starts with the fact, that all the books and magazines start to explain "background blur" with the term "Depth of Field", which is confusing matters. Depth of field actually describes the area in which the subject can be considered to be sharp. This is different from the "strength in background blur" or "blurriness" you will see in the picture, when viewing out of focus background. In your example above you will have the same framing with the 35mm lens at 3.5 feet vs. the 85mm at 8.5 feet. And yes, the DoF is the same. However the "strength of background blur" is 85/35=2.4 times larger for the 85mm lens or the background will "look 2.4 times more blurry" (e.g. blur discs will appear 2.4 times larger in diameter). If you are interested in this subject, please have a look at my article here at dpreview:

http://www.dpreview.com/articles/6091822765/background-blur-and-its-relationship-to-sensor-size

Cheers

Carsten