In the System Logs you can see whether the oom killer fired at all during that task's execution, but if you don't know to look there it can be easy to miss. We should put some indication on the main task failure page so it's more obvious.
EVG-5806 and EVG-5419 added support for checking for OOM kills in the Evergreen agent. However, these require explicitly using endpoints on the Evergreen agent. Instead of requiring users to do this, Evergreen should check for OOM kills automatically, and report on the task page and in the task REST v2 API endpoint that an OOM kill has occurred.