AWS is a Cloud Platform, just like any other Cloud Platform (Azure, GCP, etc. ), and it offers machine learning services just like the others. The ML services provided by different cloud suppliers are similar in terms of what they offer, and each has its own set of successes and failures. At the end of the day, any Cloud-based machine learning service is exactly like any other Cloud service, harnessing the power/advantages of Cloud at a significantly lower cost than typical.
Any cloud vendor-specific certifications, such as those from AWS, would indicate to a potential employer that you have sufficient expertise of that cloud platform and would advance you to the interview stage.
As mentioned mostly everywhere getting a Job at Amazon is more about competence than being a fresher or not. Whether you have a certifications or not.
With enough skill in the Machine learning domain you can easily bag a job at AWS or any other vertical at AMAZON…
All the best with your preparations.