A community or collection admin can run curation tasks against containers (collections and/or communities), however, they cannot run curation tasks directly on items. When a collection admin tries to Peform a curation task on an item, they are redirected to a "Insufficient Privileges" page.
1) It seems odd that the community admin would not be able to curate an item inside of their community.
2) If the community admin was not supposed to be able to run curation tasks against items, then they shouldn't see the curation tab on the item edit page.
Personally, I think it makes sense for community admin to be able to curate items inside of their community, same goes for collection admin.