There is a deeper issue going on here. Find out why he feels he needs to get "cool dad" points. When you get to the root of that issue, you will know how to respond.
I'd talk to him about what the law does if it finds out an adult is giving alcohol to a minor (even if the adult is the minor child's parent, they can be criminally liable). It is unfair to the kids to put them in the position of having to be the mature one in the relationship and put the brakes on their father's behavior.
This is a controversial situation. My wife would scream "Confront him hard".
I have always said teach your kids everything you want them to be by 13, because after puberty anything not already learned will be addressed in their way not yours.
Register that for a second...That being said, your husband may be addressing the fact that they are going to drink and possibly test out drugs. He could have just told them not to do it and it ended up as every other thing parents try to teach after 13, or he might feel the best way to address it and continue parenting is to demonstrate responsibility. These things would include, in the privacy of your home, to not over indulge, never ever drive, etc.
Too many teens die on our roadways, alcohol or drugs are normally involved. Most all parents just told their kids not to do it.
Examine your situation very carefully with an open mind. If you think something different is happening, tell us more of the situation and we can progress with more directed advise.