In a way, parts of the AWS SDK are already inside of Kentico in the CMS.IO namespace. You can configure the system to use S3 storage for files by following the Kentico documentation on configuring Amazon S3.
However, if you are looking to do more than S3 storage, you can add in the AWS SDK just like in any other ASP.NET project by following the Amazon AWS getting started example.
I've done both methods, they should work just fine. And if you are going to go down this path I recommend also installing the Amazon AWS Toolkit for Visual Studio it rocks.