The Zvex Nano cannot be used as an overdrive or pre-amp in front of another amp as it only offers speaker level output. Plug that into another amp's input or effects return and you will blow something up. Either the Nano's output transformer or the other amp's input stage depending on what gives up first.
The only amp I can think of that doubles as an effect is the Vox BM Special that has a dedicated output from the treble booster section of its circuit so you can use it as the biggest non-footswitchable Dallas Rangemaster clone on the planet ;)
Everything else I can think of is a pre-amp, such as the H&K Tubeman, Mesa V-Twin, etc.