I've found that most entrees at Disney are short on veggies. Lots of meats & starches, though! I frequently order a side salad just to get some greenery.
But yes, that would be an extra charge and not included in your dining credits.
If you're looking for veggies at a CS check out the half rotisserie chicken meal at Cosmic Ray's. It comes with green beans and I only remember this because so few of our other meals included any fruit or veggie at all.