If you can tolerate the lactose, why not? It's an easy source of a lot of extra calories when you're bulking up.
I'm lactose intolerant and at least mildly allergic* to milk. If I wasn't, I'd definitely drink it when I'm trying to gain weight. It's easy calories, no fuss (whey protein is fine, but then you need to mix it up all the time, which equals "fuss"), and you can easily get in some milk on top of whatever you eat instead of drinking water with your meal.
If it works for you, it's all good, anti-milk websites aside. If not, skip it, GOMAD success stories be dammed. It's all if it works for you or not.
* Yes, I know it's "rare." But I'm talking swelling, hives, difficulty breathing, etc. plus headaches and rashes for lower doses. I'm pretty sure that means "allergy."