All that sugar would seriously gunk your coils. Alcohol is not good to vape, generally speaking. Caramel is another name for sugar. In short, not the best idea, sorry...
You would probably want to avoid sugar since it would likely crystalize rather than be carried by the vapor. However, that largely depends on how much sugar is actually in it.
However....
There's a BIG difference between caramel coloring and actual caramel. Caramel coloring is simply a brown coloring, often used in vanilla products. You'll be very hard pressed to find any vanilla flavoring that doesn't have it. And vaping alcohol isn't going to cause problems, it's often used in ecigs either to thin out the juice or thin out flavorings that don't mix well with water.
In theory he should be fine using vanilla essence in his ecig juice, provided the actual amount of sugar is very low and well dissolved. It wouldn't be my first choice in ecig flavorings, but it shouldn't really hurt him or his mod any. I've known of many other people who have used it.