Yes it works, but I forgot that the method I described does not prevent users of the Read Only map from placing a new feature -- only prevents attribute updates to existing features.
However, there is another method...
Open the Read Only map and click 'Disable Editing' --found 2 places below the 'Configure Pop-up' option on the feature drop down menu. This will disable feature placement, feature movement and attribute updates. Even with this, a savvy user could still re-eable editing using this same button. For a truly read-only view, You could choose disable editing and then make a Web App (Share>Make Web Application) and choose something like the 'Legend' template. Then share the app with the Read Only Group.