Yes if Hamas uses human shields, and that is actually a war crime, which I have to believe it is but loopholes and exclusions abound in treaties, then that IS a war crime. Full stop.
Does that make it okay for others to commit war crimes?
If someone rapes or kills someone daughter, does that mean that the father gets a free pass to rape or murder the original rapist/murderer's daughter even though she had nothing to do with it other than by happenstance of being the rapist/murderer's daughter?
Just to reiterate, Hamas committing war crimes is Bad!