The OpenHaptics plugin will only apply forces to the marker point. Attaching meshes to the marker will not affect the forces applied to the device, it will still be treated as a single point.
If you just want the shovel to not visually go through objects, then you can use a physics spring to link the haptic pen to the shovel. Have a look at the following post for example code,
http://www.worldviz.com/forum/showthread.php?t=1570