My personal thoughts are there is no reason to limit pool workers, there are too many easy ways to get around it.  However, I'd say the solution is to show only their first 5 in the logs and then a note that says "57 additional: 542246 (584455)"  Ultimately even big miners are a benefit to the pools.  The way I see it, a big farm would just as well be off solo mining, they'll gain the law of averages and not have the overhead of pool communication (which is very small, but in aggregate adds up).