Is there anything wrong with roofers using employees off the clock or even you using some of the employees off the clock and on the side?
Be careful here because depending on the work being done, it may be illegal. How is payment made for the services? And who is responsible for that payment? If someone gets hurt, then whose insurance will cover them?
The biggest reason that roofers would try to perform work with their employees off the clock is to avoid having to pay the required payroll taxes. Another reason is to avoid covering them with insurance. By doing a "for cash" project allows them ease with these intentions. This is your best clue that this roofer is not a professional roofer.
A lot of repairs can be done under the table like this and no record of them will be saved. If you wind up needing additional help due to mistakes or bad workmanship, the roofer can easily disregard you. Good professional roofers do not operate like this so pay close attention to what it is they are offering you. It could cost you far more than double in the long run just to try and save a couple of dollars up front.
If the roofer tells you that he can save you money by you agreeing to pay him in cash for the work or making the check out to him personally, he is breaking the law. Maybe it doesn't amount to much from your perspective but you should realize at that moment he is not a professional. With that, what do you think he thinks of you?
Asking any of the workers on his crew to help you with some additional projects you need done, may be perfectly fine but you are responsible for their well-being during the work phase. It is not unusual to request help in this manner. What is important here is that you are aware of all the ramifications
that might impact you. Never ask anyone to do work of a nature that requires a license. If anything at all goes wrong or the work does not meet the codes, you will wind up on the wrong end of a legal dispute.