Media manager item is distributed but not used for tridion website, still it will be searched in aws cloud search?

It depends on how you are creating the indexes using AWS CloudSearch!

Typically, you can create an index from sample files or predefined configuration (if we know the indexes already) or will have to manually define them (always found that manual is easier). Once the indexes are created, we will have to populate the indexes using an SDL framework like SI4T. It also depends on how you have configured your indexes for separate languages.

If the content is distributed, you should have a mechanism to populate the search index upon publishing the media item to the respective languages / locales. If there are URL patterns are predefined, you can extend the SI4T CM framework to insert /language/locale/ specific references in your CM side and your deployer extension will pick it up to populate the data to the search index. The other way is to populate the search index upon publishing the media items to the respective languages and locales. In some cases, you will have to write site-crawlers to crawl the external DAM delivery and populate the indexes (incase APIs are not availabl).

In either case, you will have to write something custom populate the indexes correctly. Hope it helps!