1.http://wow.gamepedia.com/Unholy_Frenzy
2. a) It can be dispeled by spells that remove "rage effects".
b) Can be dispeled by gliphs that remove dmg effects on your target like: http://www.db.pandawow.me?spell=115078/paralysis gliph, http://www.db.pandawow.me?spell=118/polymorph gliph, and http://www.db.pandawow.me?spell=2094/blind gliph (just see the video to understand)
3. Should not be dispeleable at all, its a 3min cd, its not an enrage effect since patch 5.0.4: "MoP Patch 5.0.4 (2012-08-28): No longer an Enrage effect."), and should not be dispeleable by any of the mentioned gliphs.
4. fun realm
20/10 DK burst depends alot on that spell
a) video for enrage: https://www.youtube.com/watch?v=zSbNoTIV-Hg
b) video for gliphs that remove dmg debuffs on your target for http://www.db.pandawow.me?spell=118/polymorph, http://www.db.pandawow.me?spell=115078/paralysis and http://www.db.pandawow.me?spell=2094/blind : https://www.youtube.com/watch?v=HVaVJ7Vz9gQ
comment: another nerfing bug for "op" dk's