If only they could train teenagers the same way!

I think there's a big difference between trained and domesticated. Almost any animal can be trained to a degree. Dangerous idea to ever consider them domesticated though.. In the first example on that page, the day that farmer forgets to give that Hyena the herbs to curb sexual desire or the hyena realizes the livestock is edible could be very ugly.

Yes.

for how long though?, and why?

In my experience with wild animals, both carnivorous and herbivorous, I have found that any animal can be tamed if its primary instinct to look for food can be satisfied by us.
Hyenas are but opportunistic carnivores and by satisfying their food needs and eliminating their need to hunt for food - they could be tamed and domesticated.
A few generations of domestication and hyenas could be as good a pet as a dog - subject to limitations of its intelligence.

Some gang members in Africa use them as pets

http://www.africancrisis.org/.../...yenaBaboonPet.jpg