Further, if the pool is charging a mandatory fee (such as Slush) and is secretly merged mining, that's a double-whammy.
I would just like to clarify that Slush is publicly merge mining and recording all blocks. He simply doesn't have code to distribute them to miners based on proportional hashing power. Every mined namecoin block is visible w/ timestamp and those namecoins (~18K at last count) will be distributed to pool miners.
I know that wasn't your intent w/ the example but I don't want someone else confused by it.