Mentoring only works if founders can be completely open: about their numbers, their team problems, their doubts, their fundraising. They will only be that open if they're certain it stays private. Treat everything a Fellow shares as confidential unless they tell you otherwise.
Conflicts of interest are normal for experienced people. You may invest in a competitor, advise a company in the same space, or have a commercial interest in what the founder is building. The conflict itself isn't the problem; hiding it is.
Disclose any potential conflict to the Fellow and the nAItive team before you engage, and step back if the conflict is too close. When in doubt, disclose.