I don't think its true that fear helps reaper damage in any way. It would help chronos and thieves I believe. Necros have access to a trait that gives them 33% more damage while under fear (with the trade off being 250 power and fitting into the otherwise optimal build), so if there was any way of keeping good fear uptime on a boss then necros would be topping dps benchmarks (as well as making break bars trivial). (Un)Fortunately that can't be done, most classes don't have access to fear and even if you did include all the fear producing effects the dps loss from including them outweighs the gain from the trait.
I don't think its true that fear helps reaper damage in any way. It would help chronos and thieves I believe. Necros have access to a trait that gives them 33% more damage while under fear (with the trade off being 250 power and fitting into the otherwise optimal build), so if there was any way of keeping good fear uptime on a boss then necros would be topping dps benchmarks (as well as making break bars trivial). (Un)Fortunately that can't be done, most classes don't have access to fear and even if you did include all the fear producing effects the dps loss from including them outweighs the gain from the trait.