This is possible, but you'll need to find the location and package name of the of the Windows App first. Once you have that, it's easy to implement in Circle Dock.
For example, to launch the Windows Calendar, you enter the following into the Circle Dock Item Settings:
Target: Explorer.exe
Arguments: shell:appsFolder\Microsoft.BingWeather_8wekyb3d8bbwe!App
You can find the "Arguments" information by doing the following:
1. Press Win + R
2. Enter "shell:AppsFolder" to open the Apps folder
3. Create a shortcut on the Desktop by dragging the Windows Store icon to the desktop.
4. Right-click on the Windows Store shortcut and select Properties
5: The Arguments information is displayed in the Target field