I'm no expert, but these filters are designed to flow more air, so undoubtedly this will let some of the smaller particles through. As far as being harmful to the engine, i don't know. I had a K&N FIPK II on my camaro for about 4 years (40K miles or so) with no noticeable detrimental effect. And from reading some of the posts here, it seems to be a matter of opinion as to whether swapping out the stock filter is a good/bad idea. The only known issue I have heard of is over oiling the filter and gumming up the MAF sensor (93 camaros didn't have MAF so I have no first hand experience with this)
This probably wasn't much help
, but try searching some of the K&N threads for a wider discussion.