I've used a HRM to check the cal burn at a zumba class and it came in about the same burn as high impact aerobics? This was a gym class though so a lot more high octane than the zumba classes I've done at the local leisure centre? They came in as an equal burn to Dancing, general. Hope that helps?
Strangely enough the wii zumba was a higher burn than the leisure centre zumba. But I do tend to give it some welly at home lol!!