In PvP you primarily want to debuff your target, so you will end up doing BAs/FG and Ursine Brawl besides your IB. There is no room for SB.
It might be viable, if you are specced into Booming Roar and your pet already has debuffed your target sufficiently.
Furthermore you don't specc Nature's Revenge in PvP which makes SB a monster in PvE.
Imo BoN is a must have in PvP. It nets you so much energy that your whole team becomes extremely mobile. You dont even need to "hit" your Bloodflow (blue heal). In a Booming Roar/Iron Hide specc i prefer to have 5/5. Endurance on the other hand only helps yourself and even when being able to sprint more helps you to survive better than a little bit of hp reg does.
The whole point in mutilation specc is to buff up your IB damage. Thats why Mutilation is mandatory (hence the name of the build). And spending 1 more point
in Bewilder gets you a lot of utility: Safe yourself or even better your teammates from pesky melees.
About Brutal Walker: Its a decision between that, 5/5 BoN and Ursine Spirit.
As stated above BoN is pretty advantageous. So is Ursine Spirit imo. Your main manifestations should be Forest/Spirit, if you get comfortable enough with these 2 add
Mani of Sun to get some burst potential. Ursine Spirit doubles the efficiency of the spirit debuff and doubles your manareg for the time the mani is up.
I would consider taking Brutal Walker only in a mutilation specc.