Well, I don't think there a way to find out if illegal content is hosted on the website if you provide a free web hosting account to a user.
You will get to know if there a complaint logged against the account and the hosting provider informs you about it.
Generally, hosting providers to not suspend the account immediately after the complaint is logged and you will be given some time to ask the account holder to remove the illegal content
If the content is removed within the time limit provided, your hosting account won't be suspended, however, if it isn't, it will be suspended :(