With Multisites, you can either keep the VM independent or share VM.
When you share an extension, you share all its MySQL tables.
This means that you can share VM between different websites but in this case, you will not only share the product but all the store information including the orders.
We have experimented with another customer to only share the products (not the categories) but this is something that we did with billable support and managed manually.
This is dangerous and could only be done at your risk. We are not sure of the consistency and this should need a lot of test to ensure that consistency is guarantee.
If you want that we show you how to do that manually, you can order our billable support at
www.jms2win.com/download?page=shop.produ...35&category_id=1