No this approach will not work as Dashboard can only fetch live data using the web services only.
This will give you the data only at the design time only but not when the dashboard is previewed or deployed.
You have to use the connections listed in the Manage connections on the Dashboards toolbar or you can use the add query option as well.
So for this first you can create a universe and then create a qaaws web service or use query browser option.
You can go through the tutorials listed in the homepage of the SCN Dashboards for further details.