Any way to completely disable iOS passcode?
The apple configurator doesn't currently have this option.  

The only workaround I've discovered so far is to register an exchange account with the iOS device using SSL.  This forces the user to use a passcode, and disables the option to remove it.  Now go into your exchange account settings on the iOS device, deselect "Use SSL" then go and disable the passlock.  Now go back to exchange settings and re-enable "Use SSL".  You should now find that 1) the passlock is no longer enabled and 2) the setting to turn on the passlock is gone.  You should be able to disable all the sync settings so students don't start using that account for anything. (source)

If you don't have an exchange account you can use for this, set up a free google mail, and register it as the exchange account.

It may depend on the exchange server settings/policy, though, so some experimentation may be required.

Lastly, if you are using Supervised devices then the passcode will be reset when reconnected to the apple configurator.  Still more work than desired, but quicker and more painless than a full refresh.