If you towed them out for free, I would agree.
If you charged them (not them handing you a $10 or a $20 after when you didn't request anything, but you saying "I will tow you out for $20"), IMO you will be treated the same as a tow truck driver.
Thanks to subrogation (in most states), the car owner gave permission for their insurance company to sue others on their behalf to recover insured losses. The car owner has no say in the matter.
It's just like if you are injured at work and use your personal health insurance to pay the medical bills. If they find out, your health insurer will try to make your employer reimburse them for their expenses.
Aaron Z
You might want to dig deeper into this to find the not so common ways to fight them. Only reading what is easy to find and trying to work with what the laws the insurance companies readily use will keep you trapped.