You mean, web sites and databases that are already on the same system as ISPConfig? No! From the installation manual (http://www.ispconfig.org/manual_installation.htm):
wouldn't you be able to import say, a script with an existing mysql db? For example, I create a backup of an existing db from my old webiste, create an archive backup of the html root dir. Then I upload the archive and unzip it in ISPC "web" directory. Finally, I log into phpMyAdmin and import the backup sql file. Can't you call that importing?