Can we access a .NET web server using an HTTP connection on Android?
There's certainly no reason why you couldn't. The server-side technology doesn't matter (well, shouldn't matter... I guess a poor design on the web application might make it matter). If you can connect to a web server, then you can connect to a web server.
Incidentally, ".NET web server" doesn't seem entirely accurate. IIS? Apache with mod_mono? Again, from a client perspective it shouldn't matter.