I have a dedicated server running ARMA2 Operation Arrowhead.
And I'd like to use mods. For the sake of argument, let's consider the Emita Island v1.12 (@bracer).
I understand how to create a @bracer folder in my ARMA2 folder on my dedicated server using FTP.
And I understand to put an addon folder in it, and copy the files to it.

However, in the help section of adding mods, it mentions something about players needing to have
the same files in order to connect to a server running this mod. That sounds like it would require
players to "predownload" the same mod.

Is there a way I can use my redirect server so that when a player connects, and they don't have the @bracer
mod, that it downloads it automatically from my redirect?

Basically, the same way we do in Call of Duty games that are modded. When a player connects if they
don't already have a custom map, or mod, it downloads automatically from my redirect.

I hope I'm explaining myself correctly.

Thanks in advance guys. Any help would be appreciated. :)

Nope, can not be done.
However, there is a tool out there called Six Updater & Six Launcher and nowadays Play withSIX (which will replace Six Updater if I understood correct) which lets a player select a server and when the tool sees some addons are missing it will download and install those. However, it does not have all available addons and mods on its servers so it is not always possible to sync a players local install with the server installation.

Thanks for the quick response FoxHound!