Hi Wouter,
We have just released some enhancements on the OutSystems platform REST consumption capabilities that enable the consumption of some specification of OpenAPI 3.0. On this release we have not included all patterns available on OpenAPI 3.0, however, we have implemented a few that we believe unlock the feasibility of importing OpenAPI 3.0 REST web services.
https://success.outsystems.com/Support/Release_Notes/11/Development_Environment#Development_Environment_11.7.9
I'll suggest creating separate ideas for YAML and SwaggerHub.
Thanks.