Do the vocals still come through the centre channel, as they did during the famous reverse karaoke incident in 2008?
Entirely depends on who is the sound supervisor each year.
Some years it's a full 5.1 mix with centre live vocals, backing track front left and front right, and ambience in the surrounds (the common Swedish approach they often, but not always, use on Melodifestivalen) (*)
In 2014 it was a front stereo mix with silence in the centre, and ambience in the rears (4.0 or 4.1 effectively)
Other years there is a Front Left, Centre, Front Right mix with vocals spread across the three channels, and ambience in the rears, so a different 5.1 mix.
(*) Melodifestivalen stopped this method for a while as the Swedish tabloids got wise to it, and started publishing 'what they sound like live' extracts from the centre channel. Now Melodifesivalen allows backing track vocals, which are L and R, the differences in some cases were quite marked... Given that Melodifestivalen is hugely influential on ESC (as so many people from MF have worked on the ESC some years - both in production and technically - what MF does is often similar to what the ESC does)