Question regarding Uplay games on Steam.

afaik: no (uplay copy and steam copy of the same game are separate entries, and the steam copy does not permit to download the uplay copy so you still need the steam client even if you use uplay as a launcher, tested with FC BD), no (but you can add some goodies with uplay points, example maps or clothes in AC, extra songs in Rocksmith 14).

If its a game that uses Uplay and not just an Ubisoft game it will be added to Uplay and can be launched from there. As long as it's on your uplay account you'll then be able to purchase dlc there.

I bought Far Cry 3 on Steam and it's in my Uplay library as well. I can just play from there if I want, pretty sure I can also buy the DLC from there, but that is not 100% certain.
Some games with keys can also be cross-activated from Steam <-> Origin and Steam <-> Uplay. I'm not sure about which ones are applicable on Uplay but for instance --> I got mass effect 1 + 2 on Steam and could register the keys on Origin.

no and no. uplay has separate entries for steam and regular. Steam version can't be used from uplay and DLC isn't compatible.

The only thing Steam ever did for Uplay games (Far Cry 3 & Far Cry 3: Blood Dragon) I bought on Steam was giving me a key to activate it on Uplay and launching Uplay and the game for me. But from what I can remember you can just launch it from Uplay as well. Can't say about the DLC but I assume you can just buy it from them. I could be wrong though, too lazy to reinstall it to check :p

I'm getting totally opposite answers here.

Any game purchased on Steam that forces you to load the Uplay overlay will be added to your Uplay library.

I think it depends on the game, but Far Cry 3 and Far Cry 3: Blood Dragon bought on steam just gave me a key to activate through Uplay, the game did download through Steam, but I could also launch it from Uplay without Steam running. AFAIK games that don't require Uplay won't give a key.

All my Uplay games bought on steam were automatically added to my Uplay account,i have never tryed to buy the dlc's for the games from uplay for them as i figured i bought the game on steam might as well get the dlc from them as well,but i dont see any reason buying the dlc from Uplay wouldn't work.