SFLadybug, I realize it's been a while since an update from you on your mealybug problem. I googled for plants resistant to mealybugs and didn't find a list of plants. There are so many different species of mealybugs that they seem to like just about everything.
I've found the best way to fight them is to be persistant. If you are still having problems with them you might try horticultural oil. I prefer the organic Organocide that is made from sesame seeds. There is another product called Organicide that is made from petroleum.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.