It kind of depends on the milk and your dog. Pure almond milk (with just plain water) is harmless for dogs unless they are allergic to it. It’s, therefore, safer than dairy milk but it’s also not as rich in nutrients. So, it’s akin to a relatively harmless treat – neat but not necessarily “good”.
That being said, almond milk can come with various extra ingredients in it – some good, some bad. Many manufacturers put artificial sweeteners and thickeners in their almond milk which is quite risky for canines. Be especially wary of almond milk with xylitol as that’s toxic for dogs.
Other brands of almond milk are not only free of harmful additives, however, but also come with stuff such as added calcium, vitamins A and D, and more. So, it depends on the milk.