The shop I work at has successfully kept snakes and tortises in the same room for years w/o any problems; as we always follow the general rule that sick animals don't make it into the same close quarters with the healthy ones.

Now if you are talking about certain chelonians being asymptomatic carries of dieseases that are otherwise fatal in boids, you'd better start doing your research; however, I have never run into any problems in my experience with the two species.