This is not true, at least not a couple years ago. The so-called RJs are flown by Lufthansa CityLine or some such entity. Their pilots are hired as a sort of Lufthansa Lite and if they wish to go to the mainline they will have to go to a more thorough screening (selektion as it is called there) and many will not be allowed to transfer. But it's not really more thorough. It's a bit like a fraternity and if they like you you'll pass and if they don't you won't.

CRJ/ERJ pilots in Europe are treated as an even lower form of pond scum by their mainline counterparts than they are in the US. I worked over there for a number of years, which is how I know this.