Stolen phone - does Android Device Manager's lock override the thief's password?

I'm currently trying it on another phone and it seems that as long as I have a pattern lock set up, the ADM lock screen shows up but the old pattern is requested instead of the remotely set password. The stolen phone had a simple swipe lock (Android 5.1) - if the thief set up a pattern/pin in the meanwhile is the ADM lock basically useless? --- Okay, in my case the thief can definitely still use the phone - he receives WhatsApp messages and can read them eventhough I've set up the remote lock over 50 times. This is absolutely revolting - an utterly useless feature. I can guarantee he's not circumventing it another way - if they were even at the least bit technically savvy they would have wiped the phone, switched the Google account or at least disabled ADM long ago.