Does canning stock raise its temperature too high?
The purpose of using a low simmer during stock-making is to avoid agitating the liquid.  You want the fat to settle on top, but a rapid boil will simply disperse the fat and other impurities all throughout the stock, resulting in - as you've hinted at - a cloudy texture and possibly an inferior taste.

The other reason to avoid boiling is simply to prevent the stock from reducing too much.  If you're simmering for 6 hours, you could lose all the water.  If you leave the stock unattended during that time, and the water level drops too low, then you're not getting anything out of it; the water needs to be covering the bones in order to break down the collagen.

All that said, once you are finished with stock, you should have skimmed it and strained it through a fine sieve and probably a few layers of cheesecloth as well.  If you've made your stock correctly, it will be clear and have (almost) no fat.  Boiling it briefly at that point isn't really going to harm it; there's not enough fat left to cloud the stock and you're not boiling it for long enough to really reduce it.

So I would say go ahead and don't worry about the temperature.  As far as I know, nothing magical happens at 180° F, that's just a rough temperature guideline for "low simmer".