A UV detector for a furnace, fired heater, or boiler is a flame detector; one part of a flame failure safety shutdown circuit. Its purpose is to shutdown the fuel supply when it detects loss of flame.
But, the flame safety circuit has nothing to do with temperature control, which if the problem was overheating, a flame safety component or system won't solve a temperature control problem.
I suspect that the investigation team is recommending flame safety because it's a safety issue. Apparently, there is no flame safety at the present?
To the question as to whether you can install a UV detector: the feasibility of retrofit to a burner involves compatibility of UV with the fuel (spectral response), mounting, sighting, wiring for power and signal, and the requisite flame safety controller and safety shutoff valves. There can be other sensor/switches providing interlocks in the flame safety system. Vendors that handle flame safety are usually pretty fluent in their application.