If I install vm2share onto our system, the FB comments do not show up
Is there a section definition missing on the template ?

Hi,

I don't know what kind of system or structure vm2share is using. You have contact with the developer of vm2share and ask help about "How to integrate vm2share to 3rd-party Virtuemart Templates".

You might have to modify this file according to their "integration guideline"
/templates/flexible_sportmart/html/com_virtuemart/productdetails/default_reviews.php

regards