What happens if you use a non-WAAS GPS position source in ADS-B mandated airspace? Doesn't it work the same, except for the positional accuracy?
It may work. It may not work. Nobody knows. If you use a non-certify equipment when you are required to use the certified one you are breaking the law. Nobody can be sure your equipment will work as required but everybody are sure you are breaking the law.
Don't do it. You are endangering your life and others.