Yes it is possible. You have to create new symptoms which only include the drive letters you want to have alerted and then add the symptoms to the new alert. You have to leave out the drive letters you don't want to be alerted about.
Here is a blog article by Matthias Diekert in german: http://vrealize.it/2015/11/09/guest-file-system-out-of-space-bestimmte-laufwerke-ausnehmen/
and the bing-translated version: vrealize.it/2015/11/09/guest-file-system-out-of-space-bestimmte-laufwerke-ausnehmen/ - Translator