Airplanes maintain air pressure in both the passenger cabin and the cargo hold. The reason for the passenger cabin is obviously health and safety of the passengers, but in the cargo hold it is for various goods and, possibly, animals that might be in it that also require pressure. Near vacuum isn't really a good thing for pressurized containers often carried in luggage.
So, in general, airplane air pressure is maintained at about the equivalency of about 6000 - 8000 feet above sea level. So, the question you're really asking is whether or not a hamster can survive the lack of pressure at that level. Denver, Colorado, is close to 6000 feet above sea level and you can buy hamsters at pet stores there and they're not apparently suffering. While that is not really a scientific analysis, I think it's safe to say that while they might not enjoy a trip in the hold, the altitude is not going to be the big reason for their lack of fun.
I think a bigger concern, really, is that it is often quite cold on airplanes, even more so in the cargo holds, and your hamster may not be acclimated to such temperatures. So, from that angle, unless there's a compelling reason to subject it to the colder temperatures and, in all likelihood, the customs quarantine, then I would leave it at home.