When you said "real life" my mind drifted... some years ago work took me to Africa. I got to go out on a "photo safari" in a very remote place, chock full of wildlife (and yes, hyenas). Man, the hyenas really did STINK. Their teeth were amazing. Some of the spoor they left behind was like concrete -- they literally can chew up and eat bones.
I remember one evening I was sitting in the Rover in the front right seat. No windows, no doors even. A hyena walked right past me. He could have easily reached in and bitten a big piece off of me. The 375 H&H mag was on the dashboard -- no way the guide could have grabbed it in time. Anyway, it was like this Hyena knew we were there, and it chose to walk right past us -- I could haver reached out and touched its back easily. It was like he was saying, "Sup, homes" -- letting us know he knew we were there, and he wasn't scared of us.
Well, enough RL nonsense. Back to what matters, WoW:
Hyenas make fine pets, but the only special they get is Dash.
If you want a somewhat unique pet or like the looks, it will do fine. But wolves have everything a hyena has plus Furious Howl! That said, Hyenas will work. And who knows? Maybe one day Blizz will show them some love and give them a special attack such as "Bone Crunch" or "Distracting Laugh" -- or a disease attack -- or "Hideous Smell!"