I wrote to Foursquare developers telling them the Twitter and Facebook switches not working with VoiceOver. They told me that it works just fine for them, and asked me if I have the last version installed. I have, but not the iOS one.
Could you try activating or deactivating that switches from the check-in screen using iOS 7.1? I have 7.0.6 with JB, so I am not interested on updating.