Hi,
The Admirror Gallery plugin is a content plugin, not a system plugin.
You cannot add the tags anywhere you want in your website.
You can only add the AG tags in "content". So a product description, a joomla article, a category description, etc.
If you add it in the middle of a view, the plugin won't replace it. It's not a problem of HikaShop but of the plugin which is not made to do that.
You will have to change your code to force the content plugins on your tags. So you should use such code instead of what you're doing:
<?php echo JHTML::_('content.prepare','{AG}galleries/products/'.$this->row->CUSTOM_FIELD_COLUMN_NAME.'{/AG}'); ?>