I don't agree with you about Smart Burn. Look at what Nero has described SmartBurn as:
"The Smart-Burn feature enables automatic checking of quality of the disc. This may lead to lower writing speeds with certain discs, but will ensure successful burn. Disabling the Smart-Burn function may result in write errors as disc quality is not checked and the burning speed will not be adjusted."
Smart Burn has nothing to do with Bufer Under Run problems or Servo problems during write. Smart Burn checks write quality while burning and lowers the speed if required. Buffer Under Protection is active irrespective of whether Smart Burn is enabled or not.
SmartBurn limits the Max Burning speed for the medias it knows will not burn at a higher speed. I've seen 52x CD-R media which has a Smart-Burn limit of 40x and so on. So, SmartBurn has something to do with Max Burning Speed limit to maintain quality burn.
However, I agree with you saying SB and HT are two totally different algorithms. Both targetted towards getting better quality burn but, are independant of each other.