No - it doesn't fix any glitches (as far as we've been informed). Let's do some roleplay. SEGA: We have DLC! Woohoo! It adds 14 new unit types for different factions, and also will "add an extra layer to the already in-depth offering that is Empire: Total War." (Quote: Mark O'Connell, E:TW community manager). YOU, the gamer: SWEET! FREE STUFF TO DOWNLOAD?! (Opens browser). SEGA: Are you crazy!? It costs $3.50 on Steam!
Oh, SEGA. Why did you betray the gamers? For those with $3.50, the pack is available on Steam under the name "Elite Units of the West," and has 14 new unit types, available in both multiplayer and singleplayer. Thanks to Steam, the exact unit descriptions, types, and names are available online here.
Enjoy your content, and try not to encourage SEGA too much!