I'm working with Lightroom 5 Beta. Several times I tried to use the spot healing brush with my Wacom Bamboo tablet. It worked only in the first second. Then it stuck and a few times LR 5 crashed. Using my mouse to work with the spot healing brush: no problem at first sight. But, as you wrote: not so accurately.
So there must be something wrong in the cooperation between my Bambootablet and LR 5 when I use this feature. Hopefully there is a solution for this problem.