java.lang.SecurityException: Permission Denial: getIntentSender() when using UiAutomation in a test
This isn't an answer for why UIAutomator isn't catching the error, but rather a possible workaround that I found. When accessibility services are on I am unable to get an UIAutomator dump because I receive the error you described. When I turn off TalkBack and/or Switch Access in the Accessibility settings I no longer get the Permission Denial error and UIAutomator dump works successfully. Not sure if this will help you, but I can reproduce your issue every time with accessibility services ON in Lollipop(Nexus 5).
Use InstrumentationRegistry.getTargetContext() instead of InstrumentationRegistry.getContext()