Fanatics of all stripes should be questioned, no matter what topic they rave about.
Data-driven decision tables are a perfectly good way to implement complex behavior. On the day it doesn’t scale or perform to your requirements, perhaps you’ll want to consider something else.
I wouldn’t want to make a technology swap in working production code unless I had a compelling reason. It would take a lot more than fan boy lobbying.
If you’re really interested, do a PoC and get some real data. If not, learn how to politely smile and ignore them.
I’ve answered about this before:
Rules Engine – pros and cons
UPDATE: If it’s your boss, and you can’t dismiss, then make it interface based and try a Drools implementation in a PoC. If you’re using Spring, inject one and then the other, measuring performance under a meaningful production rated load. Get some real data – maybe you’ll both learn something.