Do the Windows users and groups get directly reflected to the Ubuntu base through WSL, or is there something in between?
My understanding after watching the two videos about this feature when it was announced a week ago was that nothing like that is currently implemented. Remember that this environment is intended to run as an application and every user on the system has her/his own copy. So you are free to do what you want. At the moment the functionality is simple and you should only be able to access files from inside the environment that you have permissions for in Windows.
Future versions are likely receive improvements so that when you do a fresh install of the environment it will log you in as a normal user, sudoers for example doesn't seem to be properly configured at the moment.
Notwithstanding security issues like
rm -rf C:/(WSL supports Windows filesystem access)
The correct path is /mnt/c/ (other drives or network resources were not mounted at the time), so I just ran rm -rfv /mnt/c/ and received a lot of error messages that I am not authorized to modify files in system directories like System32, but it did delete files in my user directory. Remember that a recursive option for a command is not a "security issue", a user with too many permissions who does not understand or care about commands and options to a degree where s/he chooses safer options is the actual "security risk", at least with regard for their own data.