I changed the code in the single post file to:
<?php
if(has_tag(‘video’)){
}else {
$thumbnail_args = mo_get_thumbnail_args_for_singular();
mo_thumbnail($thumbnail_args);
}
?>
So if I tag a post with the word ‘video’ then on the single post pages the featured image does not appear. This works great with that plugin
http://wordpress.org/extend/plugins/video-thumbnails