This is where it gets confusing. The software is completely free. So they intended this for people to use in VR or AR settings, like for example as a virtual avatar for YouTube. This would normally involve making money, which could be considered commercial.
However, there is a condition on their download page that says no commercial use or secondary use. It could mean you can’t sell your models themselves or can’t sell your services with the software, but it doesn’t provide any more details.
Also, it seems to export in a format called VRM, which you have to go through a few steps to convert to fbx. I assume the rigging is probably done for you, and maybe animations.
You could try contacting them here and ask them if your use case is supported. Also the VRoid site is in Japanese, but the software does support English. If you just want to try it out, you can go here and scroll to these two white buttons that start with “Win版” and “Mac版” to get the latest version.