I have worked with tea and mint in my brews before and would not recommend adding them directly as a dry hop, tea is somewhat antibacterial but not enough to risk it. Besides that, mint oil does not dissolve well in cool liquids other than higher proof booze or oil.
Two suggestions would be either soak leaves in vodka for 2 weeks, strain, let it breath a day or two to reduce and then add to secondary or at bottling to taste.
You can also brew a strong tea and use it as your priming sugar solution at bottling.
A good quality mint oil should actually be a safe bet as they often are 100% pure cold extracted and sterile. Not a chemical mix of crap like fruit extracts usually are.
Hope I helped, good luck
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