It does matter if the Keldeo has full investment in Speed (Jolly with 252 Spd EVs), as long as Keldeo is not Scarfed, you are good to go with this set.
Honchkrow (F) @ Choice Scarf
EVs: 252 Atk / 4 SDef / 252 Spd
Jolly Nature (+Spd, -SAtk) or Adamant (+Atk, -SAtk)
- Brave Bird
- Night Slash
Either nature, you are faster than un-Scarfed Keldeo.
Also, Brave Bird OHKO a Specs Keldeo.