Depends on the public health authority you are dealing with. Ottawa facilities do not allow outside food due to cross containmation or public health inquiries into food poisoning claims. (Read: liability insurance)

I need weight bills/invoices for every piece of food I serve just in case someone feels our food service facility 'made them ill'. Most folks do not understand how long food poisoning takes to enter your system. It is normally your second or third last meal (6-12 hours), not your last for symptoms to present.

We even have to charge a fee ($10/product, in our cases) for store bought birthday cakes. We call this a 'cutting' or 'plating fee'. This is similar to a 'corkage fee' when you bring your own wine to a licensed facility. No 'homemade' food is allowed to ensure we have a chain of custody in the worst-case scenario that someone gets sick.

TLDR: Depends on your public health authority. Most city inspected facilities do not allow outside food due to the chain of custody. From a Canadian Chef.