No, jurors have to swear to tell the truth when answering questions during jury selection. However, in practice if you express any reservations about police testimony you will very likely be struck from the jury by the DA.

My own limited experience on a jury is that, because of the way jurors are selected, they tend to be fairly deferential to authority (especially the judge's authority). Arguing for jury nullification or any similar concept is at a minimum going to freak your fellow jurors out, and I wouldn't be surprised if in practice they might ask the judge to kick you off the jury and use one of the alternates (regardless of whatever the legality of the situation calls for).