I've been involved in offshore activities since 1982 and have never heard of that reason - though such boots were common practice for many years. More recently they've been banned by some operators in an attempt to prevent 'twisted ankle' lost time injuries. I agree with you that having more specific controls to aid survival in the event of a 'man overboard' event' when such a fall is possible is the right approach. The type of footwear seems pretty irrelevant to survival probability in UK waters, and even where it's warmer.