I think you must contact the theme author before you are allowed to convert copyrighted and paid themes.
But..
is possible convert vB styles .. ??
It's easily possible, but you must have a knowledge of the MyBB Templates, CSS, and HTML.
the mybb templates are very versatile and i for one enjoy playing around with them ...
as to answer your question YES!
it is very easy to convert the skin BUT you must have the permission of the original creator
Please help create more MyBB themes which is similiar to vB