No, you cannot put a Ziploc bag in a crockpot. Ziplocs are simply not heat resistant enough for this and you’ll end up with chemically-polluted food and a horrifying plastic mess.
Ziplocs are made of polyethylene plastics, which start to soften up at about 195 degrees Fahrenheit, a mere 90.6 Celsius. If you stuck one in a pot of boiling water, it would quickly melt!