I would say that there are not really special dilemmas for prosecutors in high profile cases -- it is more that there is more of a temptation for prosecutors to commit violations of ethics because of the nature of these cases. As the article to which I have linked says, there is so much on the line for prosecutors in such cases that they commit very basic violations of ethics.
The idea here is that prosecutors in such cases feel enormous pressures when trying the cases. They feel that their careers are on the line and so they really have to win the case no matter what. Because of this, they commit such elementary errors as failing to notice conflicts of interest that the cases present to them.
So it is not a matter of special ethical issues in high profile cases. Instead, it is an issue of prosecutors feeling more pressure and therefore ignoring ethical considerations more than they otherwise would.