At first, of course it's possible to autorotate the EC 135 successful to the ground, also with engines still running in flight idle.
2. Yes it's true EC doesn't support AR without power recovery.
3. Yes the german army prohibited AR without power recovery.
The reasons are: Due to the light main rotor it isn't easy to control the RPM, also on the AR glide, any EC 135 pilot knows about this problem.
Yes, the blade and the rotorhub have technical problems with very high cone angles. As any helicopter pilot should be know, is the cone angle rising higher and higher if you try to get lift on the blades with a lowering rpm. But such a risk exists on AR's without power recovering. Yes, there are some expensive harms on ships after such power off AR. The german army use the EC 135 for the newbie training.
There are no problems with power off ARs on EC's BK 117, BO 105 and AS 355 Twins.