In order to disable the Dock icon, you may proceed as follows:
1. In the Finder, right-click the HoudahSpot icon
2. Choose "Show Package Contents"
3. Open the Info.plist file
4. Locate the following lines:
<key>LSUIElement</key>
<false/>
5. Replace with:
<key>LSUIElement</key>
<true/>
6. Relaunch HoudahSpot
Please be aware that the HoudahSpot menu bar will no longer be available after removing the Dock icon. It is thus suggested you configure the preferences before disabling the icon. In order to keep access to templates, you may want to enable the global menu item.