I have heard of people keeping PDFs with gecko species, but I am curious what species people have kept together. I know some people frown on doing this, but this is a curiosity question, more than anything.
Its doable but most of the true rainforest geckos commonly available such as white line, flying and tokay are big enough to consider darts as prey. While most of the smaller geckos that are often kept with darts such as Gonatodes and Spharoedactylus actually require less humidity than is advised for darts. The best species to try would be some of the smaller rainforest Cyrtodactylus Species such as Peguensis, but then you have to consider issues of animals being exposed to parasites they are not used to dealing.
If the tank is big enough and had some areas for ventilation and heat spots your best bet would be some of the smaller phelsuma species( quadricellata, V-*****, Klemmeri, etc) or possibly Lygodactylus Williamsi assuming you can still find some for sale. The last but far and away most expesive option would be the smaller uroplatus species(Phantasticus/Ebenaui)
I have electric blue day dwarf geckos and azureus mixed in my 90 gallon. They make a wonderful pair because the geckos stay up in the viv never coming down on the floor. They don't compete for food and rarely come in contact with one another. I have had the mixed tank for over a year and the geckos have breed more than a few times. They do well in the same tank together.