Well, IIRC, Lucius Malfoy works in the Ministry, so I don't think it would be all that far-fetched to have a Death-Eater amongst the Aurors...after all, I don't think they "caught" all that many, and I doubt all of them stopped practicing the Dark Arts even after publicly renouncing Voldermort.
Yet more food for thought!
One would hope the Ministry is checking their employees for Dark Marks... :-)