Petr, welcome, and I'm so happy that you're excited by Pulumi! We are a big fan of visualizing resources around here, and actually have a DOT file generator built into the CLI: https://pulumi.io/reference/cli/pulumi_stack_graph.html. Our plan is to have a "Graph" tab in the service UI eventually that would show you a nice visualization using D3 of this. Not quite UML, but we've found it to be helpful. If you come up with something, we'd love to see it and better understand what's useful in practice.

Are you familiar with the work done by CloudCraft here? I believe they have the ability to import Terraform, though I’m not sure if it’s via the HCL or the state.