I only do BG´s with my Felguard, but i am probably soon doing arena as well.
What i do for example take out a healer is, set the Felguard to intercept the healer. While Feluard is running/intercepting i cast immolate and immediatly Curse of Agony and after that Corruption. After that i cast a deathcoil which leaves
the healer first stunned than loaded with DoTs and than feared due to deathcoil.
Usually i cast a shadowburn right after deathcoil, which either leaves the healer/target with very little health, or dead. If he ain´t dead cast searing pain to take him out...works like a charm
There are two builds as i see it for arena with your felguard.
http://www.wowhead.com/?talent=IV0oZbxczIizzestxx0z
this build will give you the advantage of an instant DoT and very good
mana-control, both for you and your pet. This is especially important in long fights.
and than there is this build:
http://www.wowhead.com/?talent=IZbxczIizzestxx0pb
This build is less manaefficient and has no instant corruption, but
you have 4% more crit and abit of a push-back resistance.
The Felguards Intercept has a 30 seconds cooldown and can only be used in a range from 8-25 meters if i remember correctly, so what you want to do is either controll his charge manually and just send the felguard in and use the Intercept on an opponent who is at least 8 meters away from your Felguard, to stun him for 3 seconds and interrupt him.
Or you want to have your Felguard intercept the opponent right away.
With your setup you can use the Felguards ability to cleave at all times, since
there is no CC in your group which is broken instantly upon recieving dmg (correct me if i am wrong)