The mixed enclosures I've seen at zoos also tend to be (though not always) big. I mean that awesome roof greenhouse at national aquarium won't fit in the average u.s. house for sure.
I've also seen mixed species zoo cages of box turtles, black rat snakes and timber rattlers (Bronx zoo). What we seldom know for sure though is, are they always the same animals in the mixed cage or do they rotate them though. And, you rarely see predator and prey together, except in large tanks with sharks and tropical fish... and there the keepers tolerate an occasional snack.
And I'd like to add something. Microclimate is more than just the average ambient temperature. Of course Hemidactylus turcicus lives in the same geographic region as Amphiuma and as such is exposed to the same macro-climate ambient temperature.... you could also say that about cypress trees, eastern diamondback rattlers, and hey you could even say Florida Panther lives in that thermal environment, as do pelicans and black skimmers. That is, the temperature that the weather guy says it was that day, must be the same for everybody out there right? no... actually.. it isn't. temp under a log is different than on top of the log. temp on a rock is different. temp in the mud at the bottom of the bayou is different than under bark on a tree or under the roof of the outhouse.
Then there are microclimate issues of physical niche (aquatic, terrestrial, saxicolis, etc), humidity, etc.
and one more thing... last weekend one of my captive Amphiuma lunged at me and came OUT of the enclosure. At one point his head was at least 1.5 feet off the ground. he was leaning against the wall of the enclosure with his head waving from side to side snapping at anything that moves. Do not be deceived. Your house gecko is not out of reach. It may take time, but the Amphiuma (also nocturnal) will find him.
greg