TLDR: If the fire marshall (or whoever) says it needs to have a UL stamp, clarify if it specifically needs to be UL or if any NRTL will do.
Just as a note here (not that I know anything about this specific situation), but if an inspector says that something needs to be a UL [appliance, equipment, etc.] they usually mean it needs to be certified by an Nationally Recognized Testing Laboratory (NRTL). There are several competitors to UL (Underwriter’s Laboratory), such as CSA and ETL whose certifications are just as valid in the US. It will be marked with one of their stamps. Chances are any piece of electronic equipment you find will be marked with one of their stamps.
Basically what these NRTLs do is test the equipment to a specific set of safety standards that apply to the equipment type. Having a safety mark doesn’t mean that there’s no way it can hurt you (under normal use), but it does mean that the safety issues foreseen by the standards body have been assessed as acceptably reduced or eliminated.
Now, I worked at CSA for a few years so I have some bias about which labs do better work, etc. and I learned a lot about forged marks, but in general if it has a stamp its considered safe. There are some very very specific situations in some areas where an inspector will only accept a mark from a specific NRTL for valid reasons, but most of the time its because UL used to be essentially a monopoly in the US and its what most inspectors are familiar with.