You can keep a few species together. Some won't cross so they'd be safe. Or if you don't collect the eggs then no harm done. The worry with keeping various locales together is either fighting (which with proper species selection can be avoided) or crossing (which can be avoided with proper gender selection or only keeping 1 of each species). Your vivarium can still be done without suffering the wrath of the dart frog community. I have a number of friends that feel the same way you do and keep multiple frogs in one tank. I'm keeping them to produce more frogs so here it is one species (typically one pair) per cage.