Hello.
For convenience of users the goods in virtuemart are added to the main category and a subcategory. Whether the double address of goods auto corrects your component?
For example, the item is available to such addresses - site.com/category/item.html and site.com/category/subcategory/item.html.
It is necessary that only on they are site.com/category/subcategory/item.html
yes, JoomSEF can work according to your needs but there is not possibility to select category for generation of URL. It will crate URL with such category which is visited first by some customer.