When the Limburghuis first opened there were some nesting boxes with viewing windows (I'm not sure if those are still there) and I did see one rolled up sleeping in there.
But given that European garden dormice are nocturnal and somewhat secretive, I agree there is a low chance of seeing them awake outdoors during visiting hours.
But nonetheless I really appreciated the attention given by GaiaZoo to local and regional (endangered) fauna.
@Mr Gharial Agreed. I was only lucky on my first visit to the Limburghuis, just after it opened in 2018. During subsequent visits in 2019 I did not see any again.