I ran a quick test, and two gem generators do not stack.
Interesting that they fixed the three-slot bug.
For Tien'Chi:
You should check the sticky on strategy, there are a couple useful threads on MA Tien'chi (the wiki entry is very in depth). Baalz also wrote a guide to Tian'Chi
Here.
Most (all) nations that aren't Bless nations are vulnerable to a bless rush, especially on smaller maps. Most nations can counteract this by taking advantage of some of the early spells (especially Evocation) or keeping an awake pretender. Tien'Chi has no need of an awake pretender except (possibly) for this purpose, so it is a bit of a waster. Also, Tien'Chi's best mages have very unpredictable paths and low health, making them sub-optimal combat mages.
Every nation can be viable with some good planning and enough luck (varies depending on the nation in question). Don't let balance stop you,
