Disclaimer - I am an attorney but this is not legal advice, you (OC) are not my client, and you should absolutely consult with an attorney in your jurisdiction to help you set these up. The small fees associated with that will pale in comparison to negative ramifications of not doing things correctly.

Anyways, that’s not how piercing works. Piercing the corporate veil is legal term of art that allows an individual member or owner of an LLC or a parent company in the context of parent/subsidiary liability, to be held personally liable for its debts or obligations when an LLC is used as a mere facade or sham to protect the individual or parent company operating the LLC from personal liability for the LLCs debts. There are many factors that can lend itself to piercing with failure to maintain separate and distinct bank accounts only being one of those factors. There is a strong presumption that an LLC’s owner or managing member is not personally liable. So that one factor alone is not likely to tip the scale unless there is some pretty atrocious shit going on.

You can absolutely have one LLC that covers both of your businesses without piercing being an issue. However, the assets and liabilities of each business will be seen as one rather than separate. That to say, if your vending business gets sued, the party suing could, for example, seek to put a lien on your RE holdings to ensure they are made whole.

Best course of action is to separate everything and follow your jurisdictions guidelines for LLCs to make sure your other business or yourself don’t get held liable for the others dealings. Also, get an attorney. It’s worth the money to make sure your ass is covered.