I've just been looking into this - looks like there's MX controls that will work on an M device:
Also, if you're using EHS you can just stop the dialer being shown at all by disabling the dialer application - add <application package="com.android.dialer"/> to the <apps_disabled> section. Only works as long as you don't use it elsewhere!
If you're using EHS - I would set the <bypass_keyguard> tag to 0, because this EHS feature doesn't work after KK i found it makes the performance (removing the camera icon) inconsistent.
Hope this helps!
Unfortunately the lock settings in MX just seems control the security functions like swipe, pattern or pin. I don't see anywhere that allows you to remove the shortcuts like the camera and the emergency dialer buttons. Does EHS control the lock screen or just the launcher?
You can lock down the camera shortcut from EHS but I've been fighting the same battle on trying to remove the phone icon from the lockscreen....
You used to be able to disable the Lockscreen (keyguard) using EHS too but this doesnt work since L, Google changed what they support and the fact phone icon is there by default....
SES team did a piece of work that allowed you to remove the lockscreen but that might not be what you're looking for, i'm using this with a customer while I try and figure out a better solution!
Maybe trying to control the phone numbers which the dialer can access by managing the device phonebook....will see whats possible....