There are some tags that might be useful for what you are trying to ask about, but each one has a slightly different focus from what you are asking as it would be "opinion-based" to ask a broad discussion about whether someone uses something. For all of the following things I want to recommend our Sandbox where you can test a specific question if you are not sure about whether something would be on-topic or not.
The tag worldbuilding-process explains in its tag description that it can be used for questions that fall roughly into the following category:
the world building process covers how to build a world including ways to execute repetitive tasks
This tag might be useful for you if you want to learn how other people go about creating their world, or, to make it more on-topic, how you should go about creating your world once you enounter a problem or are not sure how to proceed. I would imagine that asking about the Pros and Cons of using an entity relationship model for managing the relationships of characters in your story might make for an interesting question that would be helpful for others. The wording is important there, as you don't want opinion-based brainstorming, but somewhat objective answers.
You could also just ask about what people do to manage the relationships of their actors. That would give you a broader view where people are not constrained to UML, which might be useful to broaden your view on the topic. Here you should be careful not to make it "too broad".
Here are some examples from this tag:
This is probably the one that comes closest to what you are trying to achieve.
The tag worldbuilding-resources is
about books and technological aids to be used for hastening the process of designing and fleshing out your story-setting to make it as beautiful, believable and engrossing as possible.
This tag might be useful if you want to learn which tools you could use where "tool" is used in a very broad sense. It is often used for recommendations of for example websites or books you might want to have a look at to learn about your topic. I would imagine that asking about resources where you can learn how to use UML for WorldBuilding might be a good question where you get a lot of links and simle explanations to sites explaining this topic in greater detail. Questions with this tag would be more focused on the resource itself and not so much about whether someone here on WorldBuilding.SE uses it and what the good and bad things about your approach are.
This is probably not quite what you are looking for, but might be useful at a later stage to get more resources.
This tag might be useful if you want to see what software you could use in the context of your specific question. I would imagine that postulating that you want to use UML and asking about which tools are out there for working with UML maybe even with a focus on WorldBuilding might be on-topic.
This tag might yield good results, but you won't get a lot of feedback on whether it's a good idea or not and you probably won't learn a lot about what others do in this regard or where you can check online for informatione about the topic.
I think a question about this would be useful for the site so that others can see how you want to go about this topic and to have resources if you are having the same idea. I think the tag worldbuilding-process would be useful for what you are trying to do as a first step, but depending on your concrete interest other available tags might be more useful. If you want feedback on a question draft the Sandbox and the chat would be the appropriate places to ask.