The judge can dismiss jurors as well, and probably dismisses most of those that get dismissed, most of the time. Each attorney usually gets a specific number that they can dismiss "without cause", or they can ask the judge to dismiss one for cause. The judge doesn't have a limit. I know it doesn't sound fair, buuuuut.....
So if an OSBI employee was on the juror, the judge allowed it and the defense attorney probably did, unless he/she was out of dismissals. Most prosecutors probably wouldn't object, unless there was some other reason.
Probably so, as I sat for jury duty once, although I wasn't even "interviewed" by the attorneys. They picked the jurors and alternates before they got to me. One of the agents of the OSBI was at the prosecutor's table while I was there and told me later that they would have rejected me because of my employment with the OSBI.