As long as the supplier does not call on you and you have no influence over the supplier’s business relationship with Walmart, there is not a conflict of interest. If the supplier does begin calling on your area, you should disclose the relationship to your management team and work with them to resolve the conflict.
If there is a legitimate business need for meeting with the supplier or potential supplier, you may join them for lunch or dinner meetings as long you pay for your own food and beverages. It’s important to remember that you should treat each supplier fairly. If you meet one supplier or potential supplier for lunch or dinner, then you would also need to be open to meeting other suppliers or potential suppliers for lunch or dinner.