That gets a little complicated. The short answer is yes, but the are not any security measures preventing heap dumps from memory access violations. If your application is on the device, it can cause a dump and grab the info from it.  

 does this require an exploit in the app itself or is this an exploit in linux LXC namespaces? 

 Neither. This is a weakness in how the JVM responds to invalid memory access. While there are some security issues existing in the LXC namespace, they do not correlated with this issue.