"Is a pot-smoking JW really a JW ... "? Provided the person still considers herself/himself/itself a JW and is considered by the congregation to be a JW, then the answer is yes, in the same sense that a JW elder who sexually abuses his child is still a JW elder - until the religion designates him as no longer a JW elder.
Likewise a JW who habitually fornicates (unknown to the congregation) and who habitually smokes tobacco (unknown to the congregation) and who steals (unknown to the congregation) and secretly has some doctrinal beliefs which the WT considers apostate, but who thinks of herself/himself/itself as a JW, is active in field service, and attends JW meetings, is still a JW - until the religion designates the person as no longer a JW.
Yes in these examples the person is breaking major rules of the WT/JW religion, but by the definition of the religion (and also in the mind the person claiming to be a JW) the person is still a JW.
If someone answers "No" to the question of "Is a pot-smoking JW really a JW ...?", then that person is committing what is called the "No true Scotsman" fallacy. See https://en.wikipedia.org/wiki/No_true_Scotsman for more information.