Without knowing for sure, my own personal theory is that the posts will never get hot when running the ESC.
It's the various components inside the ESC that will become hot and that's why there's a heatsink and a fan to battle the buildup of heat inside the ESC.

So I doubt you have anything to worry about, putting shrink tubing on the soldering posts is a good thing, it will prevent any mishaps where something bridges between the exposed posts and a short circuit happening.
I'm a big fan of shrink tubing and anything that will help protect soldering posts and plugs from having any exposed areas that can create problems.

But this is just MY personal opinion.