Apparently this haste increase is gained by killing pets as well. I know that most of you are PvE players so I assume you know something about this. Does the haste only increase rune regeneration or does it actually affect DoT's and the Gargoyle? If yes this ability could be ridiculously overpowered when fighting Warlocks. You just need to spread diseases and have the pets in DnD to get them to 50 % HP and then just Soul Reaper and kill it. So if I have all procs up my damage, especially from the gargoyle will be tremendous.
Does the haste only increase rune regeneration or does it actually affect DoT's and the Gargoyle?
As previously said haste doesn't scale dots. Melee haste doesn't improve Gargoyle either, he needs spell haste, so from 5% raid buffs and 30% from bloodlust. It also takes a insane amount of spell haste for there to actually be a benefit. Gary will always cast one Gargoyle Strike, wait a sec, reposition, cast the next Gargoyle Strike. This lag between strikes mean even if Gargoyle Strike's cast time is reduced, it still takes the same time between nukes, so you end up needing bloodlust and 5% spell haste just to gain one extra Gargoyle Strike over the whole duration.
So overall, no Gary doesn't scale with haste reaaallly. As much as we'd love him to.