I might be wrong, but I think Guided Access and Single App mode, whilst using the same frameworks, are subtly different. Apple themselves refer to single app mode (http://support.apple.com/kb/DL1682) and most MDM sites talk about single app mode policies.
I've experimented setting Single App mode in both Apple Configurator (where it's called Single App mode) and via Airwatch and when done in such a manner there isn't a password, nor does the triple tap of the home button allow you to exit it.
I've done some more research on this and from what I gather, the act of hard resetting it will just bring you back to the home or lock screen and not straight back to the single app mode, and this is by design. I accept admins need a way to regain access to the device, so I will just have to accept that any users doing this are doing so maliciously to try and circumvent single app mode.