Personally I would not do it. It's much easier to monitor the individual animals health when they are separated. Also you never know when those animals who have gotten along suddenly decide not to and good chance I would not be around to separate them before injury.

However I do have two crested geckos: non breeding and non prey eating females who currently live together. Oddly enough I had the one and she was doing great. I purchased another from a breeder that had been living with another female. Once she arrived and was living in quarantine she was not eating and losing weight. Geckos can take a little while to settle in but i was concerned because our others had quicker adjustment times. After a few weeks and after talking with the breeder we took her to the vet. We got deworming meds and after another month we got her weight to hold steady. The breeder had mentioned she lived with another female and we both wondered if it was possible she was lonely. We waited another two weeks while her weight held steady and placed her with the other female. We changed the enclosure around and changed the bedding and gave them more hiding spots and two feed dishes.
They were checked daily and weighed weekly. In the first week she gained two grams by a months time she gained 10 grams. They are still living together and both are doing great. Checked over every few days and weighed biweekly.
So for some species I guess it's possible.