MacOS – Windows authentication to sql server

I'm not aware of a way to make them show in the list, but you could just type smb://servername/sharename$ in that box, if you know the name of the share.

In that initial Connect to Server window, you can also click the + icon to bookmark it in the list below the text field. That way, you don't have to type it every time.

Alternately, if you have a bunch of them that you mount together, you can create an Automator script that will mount them for you, provided you know the share name for each. I wrote about that option in an answer to another question back in October.

I've never tried any of the Mac Server products. But AnandTech has a pretty good in-depth review of Mac OS X Lion Server. A few of the conclusions:

...server administrators will be happy to know that, in spite of its deeply cut price and consumer-friendly distribution method, Lion Sever stacks up favorably against Snow Leopard Server.

and

OS X Server is most useful in a handful of different scenarios: the first is that you have a small network that’s in need of a full-featured but easy-to-manage and simple-to-license server product. The second is that you’re managing a network of any size that used to be all-Windows, but hosts a growing number of Macs (this is often the case in education, for example) - OS X Server knows that it’s going to be finding its way into a lot of Windows houses, and as such it integrates fairly well with existing Active Directory setups. The last is that you have a bunch of iOS devices flooding your network and you have no idea what to do with them - iOS management may be Lion Server’s ace in the hole.

(emphasis mine) Seems to fit your intended usage pretty well.

About your other question:

Besides, and this is a bonus question, do you have some experience in using Lion server to manage centralized Xcode development? (we currently use our own MacBooks and we keep in sync using Git, I'd like to know for different approaches based on OSX Server).

Keep using git, use the OSX server as central repository (maybe consider buying GitHub Enterprise or using an free/open source alternative for managing your git interaction). Install a CI-tool (Jenkins or similar) on the server and use it to create automated builds. Should work quite nicely.