They support vcut
http://support.seeedstudio.com/knowledgebase/articles/912045-v-cut-rules
but i read somewhere they manually check before proces. Some houses are not amused with overlapping holes.
It it just a text-line in the GML file?
Maybe someone could give a example when a 100x100 size has a vcut between a ex. 40/60mm sub-board?