That sounds like a great idea. I wondered when somebody would try that and I considered doing it myself. Emersed aquarium plants are so easy to grow.
The easiest way to do this would be to just fill the bottom of the enclusre with Aquasoil or somthing similar. If you want any kind of built-up structure inside you will need to have very good watering or misting because those areas will drain much faster.
The plants might appreciate some air circulation so as long as you can set it up without drying the air a little CPU fan could be helpful. A fan aimed at front pane of glass will reduce condensation some, but you will probably still get some fogging. The condensation correlates with the difference in temperature between the room and the inside of the enclosure. the colder the room relative to the tank the more condensation you will get.
This sounds like it would be a pretty simple setup. I would probably just use a regular aquarium instead fo the Exo Terra.
My main reason for the exo terra is the opening front so I can work on it and take pictures if fogging is an issue, I plan on mounting the mister and fan to the top (I'm thinking a knife type of return that will blow air across the whole front of the tank, I was just going to recirculate the tank air so it doesn't dry out). This with the lights will make getting into it alot harder than just being able to open the front door and work on it. A tank would be a much cheaper solution though. I also want a taller tank 24" or so and really don't need the thick glass that an aquarium that height would require.