The main issue is trying to get a useful view of the overall memory used by the main process and content processes. The naive implementation of summing the RSS for all processes is going to make things look much worse than they are. For the measurements I've been doing w/AWSY + e10s I settled on:
overall_memory = main_rss + sum(content_processes_uss)
So at the very least you'll want to add 'residentUnique' to the probe. Currently this only works on linux (I think), I'm about to land a patch for OS X as well. If necessary we can prioritize adding it to Windows as well.
I'm not familiar with the telemetry probe, but you'd need to make sure it's reporting from all processes, not just the main process.