Stargate SG1 - The Fifth Man

SG1 need to rescue Jack and the non-existent Lt. Tyler this week on The Fifth Man. Have we uncovered the reason that Lt. Tyler HAD to be played by Dion Johnstone? Just what is Simmons up to? Is he really trying to shut down the SGC? It would have been really interesting if everyone "remembered" a different face for Lt. Tyler. Also so many missed opportunities to play into the 5 of this episode.