If you're on PvE like myself, you're going to need to first bola the alpha and then gate it in with 4 wooden Dino gateways and their coinciding doors. Just make a square around them. Then, wait for the other hyena's to be a far enough distance from the alpha/cage and then cage them in as well. I did each hyena individually because they spook otherwise.
A word worthy of note, Hyaenodon's WILL attack in large packs. Stick to a group of three, including the alpha.
Also worthy to note that alpha's occasionally enter some sort of rage mode and can quickly break free from bola's.
After you've got your hyena's caged, fly out of render distance to lose aggro and then fly back in and proceed with the tame.
You still need your ghillie suit and to be crouched.
These are only one time uses so make sure to demolish for resources after you're done!
Normally you can't tame the pack leader, so just get a pteranodon or argy, pick it up and drop it in a large area (like a separate section of your base). When you take it away from the rest of the pack, it removes its 'pack leader' title, allowing you to tame the highest level hyena of that pack.