There are always a few who won't comply, but the vast majority of MH's over 3.5 tonne comply, both French registered, and those registered elsewhere. It's certainly not true to suggest most the French don't bother with them.
I know someone with a 10 tonne ex army truck conversion, he hasn't been pulled up yet on a few trips through France, but my money is on, he'll be paying a fine one day.
If I remember correctly, the breathalyser rule only lasted a short while, before being revoked, because of supply issues. The angles morts have been in for 4 years and there is no shortage of stickers.