I'm not positive, but I think this isn't implemented right now in the API. What you could possibly do is to use the embedded Log Insight agent to get those logs over to a Log Insight environment, then use its API to query for the events you want. Pull down the Content Pack for vRA so it has the correct parsers and agent groups, then you get at those logged messages much easier and quicker.
Yeah I though so much and would like to use Log Insight, but have not been able to deploy an instance yet, hence the question about a direct way. Will try it with Log Insight in the near future though.