Yes you can.   In order to use your own icons, you need to do the following:

• Load into your Joomla Root/components/com_gmaps/icons folder. 
  
• Go to the GMaps control panel in the backend adminstration panels
• Select 'Manage Icons'
• Select the icon name (this is retrieved from the filesystem)
• Specify the icon height and width
• Click 'Save'

That's it.

This was changed from the initial version due to a changes in the rendering class to ensure the icons would display.