The problem I see with mixing with frilleds in a terrarium is that they're all over the place. They're not strictly arboreal, they're not strictly terrestrial, etc. Also, your 175 gallon reptarium won't keep your two frilleds for that much longer, espesially if you want something else in there. You would need a pretty large terrarium for two frilleds and something else.
:Have you mixed desert with tropical? Which?
Would that be possible? How could you supply two types of environment in one terrarium?