It is just a requirement to be there, your mode of travel is your decision to make. If you don't make it, there's no excuse. But I suppose that's normal.
Regarding fast trains: you'll only have a TGV connection into LUX. From the German side everything goes via Trier. Not being familiar with the German part, I suppose you can go fast until Trier, and normal afterwards to LUX.
Mostly people drive from f.e. Cologne, and leave some time before their expected wake-up call. Mostly it's spot on, but if the wake-up call comes later than anticipated, they'll have to spend some hours in the crewroom.
Also in winter time they allow more time for travel, which can make it a pretty long day.
As alternative you'll find crewmembers sharing an apartment in Trier or surroundings, costing them maybe 150EUR all-in per person.