Is yoga good for helping herniated disc pain?

Yes. Relaxation is important when there is symptoms from a herniated disc. Yoga can help relax and this could help release any additional pressure. Important to note that often other measures are needed to relief symotoms from disc herniation. This includes injections and surgery.
No. Be careful. Positions which require flexion or bending at the waist can exacerbate symptoms associated with a herniated disc and increase your pain and cause or aggravate sciatica (pain down your leg from a pinched nerve). In my opinion, if you want to participate in yoga you may need to modify your program.
Yes. Yoga styles that take into account the particular issues of people with spine issues can be very helpful. The core muscle strengthening and stabilization can be very effective in pain control.
Yes. I am not a fan of alternative medicine, but I am sure that any technique which focus your mind on something other than your pain would be helpful. Dr. J.