What types of bugs are generally considered release blockers?
Issues that affect the critical path stuff (graphics, installer, network) have a lower barrier because fixing them with updates is much less optimal.
Why aren't sound or audio bugs considered blocker bugs?
Sound issues have a very high barrier to being release blockers, because they can be fixed well with an update.
I have identified a bug that I believe is a blocker. Is it okay if I just add it?
If you have reviewed the blocker criteria for the release and believe your bug meets the criteria, definitely add it. When in doubt add it to the blocker list. Better to add it and have it removed versus never getting a thorough review.
What is the Target Release tracker bug for?
The Target tracker is a nice to have list of bugs for a release. It is a convenient way to separate them from all the other open bugs a maintainer may be following.
Is there a list of all the blocker bugs for a release?
Yes, Tracker Bugs