Zumba isn't necessarily "high impact", but it can be very hard on your joints. It can be, depending on the instructor. Lots of jumping around.
Walking is low impact, and a great way to lose weight. Given that losing weight is primarily about nutrition, and not so much exercise (you can't out-exercise a bad diet) it's very possible to lose weight even with mobility issues.
Honestly, there's not much we can advise you on, given your medical condition. Only a medical professional who can examine you and consider your medical history can really advise you on that!