In case you have any question about just "chancing it" and they catch you without telling them first, here are what the Terms and Conditions section says (and I took this from Full Tilt .net just in case they had different terms for play money only)
......4.2 PERSONAL USE.
....... The User must provide full and truthful information regarding his/her legal name and identity when such information is requested by FTP. A User may not have more than one account with FTP. Violators of this rule are subject to an account review, which may result in the suspension or termination of all accounts.
......4.5 FRAUDULENT BEHAVIOR.
In the event that FTP deems that a User has engaged in fraudulent, unlawful, dishonest or improper activity while using the Software or playing the Games, including without limitation, engaging in any of the activities set forth above or any other game manipulation, FTP shall be entitled to take such action as it sees fit, including immediately blocking access to the Games to such User, terminating such User's account with FTP, disclosing such information (including the identity of the User) to any person or entity that has the legal right to such information, and/or taking legal action against such User.
PS You could go years before they ever find you out, BUT they generally find out when you have built up your account to $10,000 and request a withdrawal