I highly doubt that your hops will pick up any character from the onions or mint, but those are two very difficult plants to get rid of. I would first excavate as much as you can and try to remove any bulbs and rhizomes that you find. If you do a thorough job, you'll think you've gotten rid of everything but some will most likely pop up next season. It can take a year or more to completely get rid of that kind of stuff so be diligent. ps: the herbicide treatment usually only makes you feel better about yourself, and that only lasts until the weeds begin to regrow. Hoppy Growing!