There is NO SUCH THING as a safe engine all engines can do damage.
Some will do more than others occasionally even an engine that will do damage actually wont but its nothing to do with being safe its just totally random.
As an example when i was working on taxis with the 2 litre 16 valve engine we had quite a few broken belts over the years sometimes it would break 4 rockers sometimes all 16 but twice we had an engine with NO DAMAGE new belt on and off it went its random nothing to do with safe or unsafe interference or not its just sheer luck
My sons espace threw its belt last week and we fitted a new belt first just to know extent of damage it started and ran but was popping so stripped out camshaft 1 of the 12 rockers broken i have seen them break all 12 rockers again its just luck
The DV6 engine you have is the same as stated above IF the belt breaks its the rockers that get the damage no bent valves etc contrary to what most garages seem to think its JUST rockers this is true of most modern diesels.
Petrols on the other hand will nearly ALWAYS bend valves this is due to the fact the valves are angled on a petrol.