If you can show a crime such as abuse or health concerns, yes, you can and should report them.
No contract can be used to cover any form of criminal activity, it becomes void in any court or litigation's.
It could construed a crime in itself if its intent is to cover wrong doing.
Your largest obstacle here is lack of proving any mistreatment, most authorities take that as hearsay, and not grounds for probable cause.
You may get ASPCA to investigate, but nothing would change without substantial proof of your claims, and this would not go anonymous.
Take the matter up with the county this business is licensed for. Consider also, one of the first things under the microscope is disgruntled employees, if you are just looking to 'get even',it can backfire terribly.