Most servers typically use stable versions like 1.6.1, 1.7.1, etc. Sometimes players might host a private server on a nightly build but everyone has to have the exact Nightly version.
Another thing is that some servers are hosted for Patch Packs like JGR Patch Pack. typically those are more often hosted by random people and not as a dedicated server on a seperate comptuer.
Lastly, if your talking about the thing you see when you open the game and it loads/checks stuff before the Main Menu appears, thats just the game checking where all your NewGRF mods are and what you have. If you have many NewGRF's that can take a moment or two depending on how good your computer is (I play on a Quad Core AMD CPU and it takes about 10-20 seconds to check all my newgrfs before the Main Menu appears)
NewGRF updates form the content downloader by the way are up to the NewGRF developers, they can update their GRFs as often as they need to if they want to add new features (and bugs
) and fix/break things.