Yes. An application can be submitted once the necessary information to request the letter of recommendation has been provided. The letter writer can upload their letter, even after the deadline you set on the request has passed. 

The institution will receive your application as soon as it is submitted (with the status of Complete, pending letters) and have access to review all submitted materials. 

A pending letter request will show in your materials with the status Pending: not yet received.

The institution cannot reach out to any of your letter writers, but they can reach out directly to the applicant if they have questions about the status of your pending letter request.