I'm afraid the documentation for 3.x is incorrect here, the dateTime function uses the timezone of the session of the user and the dateTimeUTC function uses UTC as a timezone. If you are doing this in a scheduled event (with the system session), it will use UTC as a timezone. In 3.x we have made sure that the timezone the server is running in is irrelevant for everything but scheduling events at a certain time. In our opinion the location of the server in the world should not affect anything else. For more information on date and time handling in 3.0, see https://world.mendix.com/display/refguide3/Date+and+Time+Handling+in+3.0
I will update the documentation for 3.x accordingly. Do note you were linking to the 2.5 documentation though, I won't update this version because the text is correct there.
Edit: updated documentation is here: https://world.mendix.com/display/refguide3/Date+creation
However there shouldn't be a difference between dateTime(2011,1,1,0,0,0) and dateTime(2011,1,1), if there is I recommend filing a ticket so we can have an in-depth look. I could not reproduce this myself.