If anything is going to pollute the jury pool, it'll be the video of the crime.
But, this case didn't generate all that much interest until people all across the country viewed that video, and then there was an explosion of public outrage over what had taken place. And I think that outrage is what the D.A. has been responding to with his remarks, and his vow to try this as a hate crime. I don't see that as "grandstanding", he is trying to assure the public, an outraged public, that justice will be done for the victim of this crime.
Obviously the D.A. believes Dedmon is guilty--he's charged him with murder. So, the D.A. is not obligated to engage in a charade of pretense about this issue. And Dedmon's remarks justify the D.A.'s assertion that this was a "hate crime", so I think the D.A. has a right to make those remarks public.
Because the video is such damning evidence, the only real issues to be decided are manslaughter vs murder and whether the act was a hate crime under Mississippi law. On those issues it may well be possible to find unbiased jurors--not everyone follows the news or follows it closely enough to form an opinion.