Of course you all know that I am not affiliated with SO in anyway and have no authority to make any statements regarding any trademark legalities.
With that said, let me go ahead and say something anyway.
Joel has stated, in other questions regarding trademarks
I am going to take a swing at interpreting this in the context of your question and then see how it all shakes out.
I would guess that re-using non-branded UI elements will be acceptable as long as the use does not contribute to an effort to mimic an SE site's 'look and feel' so as to confuse any reasonable person as to the origin of the application.
I will also assert, publicly, that the minute someone with the authority to do so, states that the use of a bullet using the same colors as on SE sites is a trademark infringment is the minute I never visit another SE site or push a single bit that has anything to do with the API.</dramatics>
of course, i only say that because i know it is just silly and will never happen. I still have way to much faith and respect for the upper echelon of the SO team