How do I use a theme hook suggestion in template.php?
The default theme function for all fields is (wait for it), theme_field().  You can copy this function into your own theme, and rename it to MYTHEME_field(), either to alter or to refer to as reference.

You would then name your specific version MYTHEME_field__field_video_virtual_tour__basic_drealty_listing().  Note the two underscores separating the parts.

For reference, the standard suggestions are


MYTHEME_field__FIELDNAME__CONTENTTYPE()
MYTHEME_field__CONTENTTYPE()
MYTHEME_field__FIELDNAME()
MYTHEME_field()


Also remember, these are really just to wrap your elements with some HTML.  If you want to change the way the element itself gets rendered out, you should really make a field formatter.