If user becomes a vendor, then I believe they have to select a category type, not sure if they have to reenter their personal information. But there might be more information you may need from them and have them select attributes to display on their vendor profile.
The category is displayed on the vendors profile if you set up a vendor/host page. It will be displayed as a radio button to select the category to search for the vendor/host.
I believe a category is required, but the hivepress team can elaborate further if it is possible?
Remember there are various uses for directories, so maybe it does not fit your vision, but it might fit some else for their use case. There might be a way to modify it with customizations. However, the hivepress team normally only gives basic code snippets (there are already over 100 to choose from), but not sure if what you are requesting is considered advanced customizations. If they give a code snippet for every unique case, then they wont have time to work on advancing the general road map they have approved. Read this it will give you code snippet to delete the vendors from having to select a category: Disable Vendors From Selecting Their Category - #7 by yevhen
If you want to add a code snippet to display the category on the vendor/host page read this: