I am looking for a tool that will present a microservices diagram from a YAML file or create a file that I can import into something like Visio.
How about converting to JSON first with something like https://codebeautify.org/yaml-to-json-xml-csv
and then use json-to-plantuml. You can test the output with http://plantuml.com/. I don't think there is a silver bullet so you might have to tweak the output to get what you want.