I have to confirm Jan's findings, when setting up an ECL provider, you specify a
PrivilegedUserName for each mountpoint. If that user is a SDL Tridion Administrator, then your mountpoint should work for all SDL Tridion users.
For my mountpoints I always use the SDL Tridion Admin user for that, which also is a Administrator on server level. Depending on your ECL provider of course, but in general I don't think that would matter, as long as it is a SDL Tridion admin.
So besides from setting up a valid
PrivilegedUserName, the only other requirement for each ECL provider is that your users have to have read rights on the Stub Folder(s) which you specified in the mountpoint configuration.
If your Authors don't have read rights on the stub folder, that will hide the mountpoint all together for them.