More than likely they did, sync boxes have been around for a long time, they're not that expensive (would have been in the hundreds of dollars or euro at the time), and Daft Punk could surely have bought or borrowed one if they wanted. I was just having a chuckle at the blog author's idealism about how well sync works in the real world. If they were using MIDI, the standard allows for a 1% timing variance at the hardware level (not 1% of 1 beat, 1% of the tempo). I would guess Daft Punk were more likely using old 'classic' synths with control voltage, which is often a bit more reliable.

Why not? It’s a common equipment and it’s not count as "digital device forbidden in analog studio" as you connect synth directly to it, just to make sure that your front waves are in sync