This is a true story. Take it for what it is worth but I will live by it. I smoke a lot of pork, fish, venison, beef, turkey. I was always of the understanding that hard woods only should be used to smoke. And under stood to never use a tree wood with needles or that does not lose its leaves. Apple, pecan, cherry, maple, hickory, mesquite, only. I have lived by that for 50 years of smoking. So hear is my true story for you to decide.
A very close friend of mine stopped by my camp one sunny fall day after his morning hunt. He had been hunting on some state land next to my property. He drank a beer with me and he offered me some jerky he had smoked with his favorite secret recipe. I tried a taste and it did have a very distinctive flavor which I had never tasted in jerky. He shared his secret with me. He said the secret to the "tangy taste" was hemlock wood for smoking. Bark included.
At that time I swallowed the piece I was chewing and when he offered me more I politely declined.
I then told him that I had always heard that soft woods and hemlock in particular were never to be used for smoking. I told him I always heard it from the old timers (of which I am now one) and that I had read it somewhere (but could not remember where) that it was really full of carcinogens. All smoked meat may have a little carcinogen in it but that hemlock was really BAD!! My friend laughed out load and said " I have been eating his jerky about 10 pounds a year for the last 20 years and it has it hasn't hurt me yet." I said "Check it out if you get a chance. I read it somewhere on the internet I think." He said he wouldn't bother because if it hadn't made him sick yet it sure as hell wasn't going to. He shot 3-4 deer every year and ate a lot of it year around.
He died at 48 from stomach cancer. Coincidence? I am sticking with hardwoods.