Could I have a bonsai tree in a firebelly newt tank?
 

Since there wont be much land, I want to get a bonsai tree there and train the branches to go over the water. I don't think I can have this with just sloping gravel up to the side so Ill either have to divide it with a piece of acrylic or whatever and silicone or have it potted and use that as the land portion with a driftwood bridge up or something.

I don't think they'd try to eat the plant so is there any reason why this wouldn't work?

Many types of wood will grow mold in a tropical environment, especially if the wood is touching moist substrate. Some people wrap the base of their wood in a safe plastic to avoid mold. Also, you have to be careful what driftwood you use. Suprisingly enough, there are products labled driftwood that will mold easily.