Hi Karpura -
Tableau Server is device-aware in that it understands when it is talking to a mobile device (an iPad, for example) and will activate a "mobile mode" which includes finger friendly mobile gestures.
However, it does not change the layout of a report on a per-device basis, which is what I think you may be interested in. I'd suggest creating a few versions of the dashboard sized to different form factors, and point your users at the appropriate version.
Hope this helps.