Here's a script which I think should do the job, assuming you have a filter set up to move all incoming mail to a label called 'hidden_mail' (warning: untested!):
function checkMail() {
GmailApp.moveThreadsToInbox(GmailApp.search('label:hidden_mail'));
}
Just create a new project on https://script.google.com/ , paste in this code, and then Edit > Current Project's Triggers and add a trigger to run checkMail() on whatever schedule you want.