I have heard a number of APMs create "spans" (distributed tracing lingo for an operation) and aggregate them for reasons like latency metrics.
In a way, Zipkin does this. The ever popular service dependency diagram is an aggregated view of parent/child links between services with the number of calls between them added for color.
The biggest issue with using a tracing api to back metrics is that most of the time, tracing is sampled (like 1 out of 1000). Sampling is done to reduce costs or prevent a surge of traffic from taking out the