A lite coat of oil on the spring and buffer would do no harm, nor for that matter no good. Sure there will be some crud attracted to the oil but it shouldn't be an issue unless you only clean your weapon every ten years or so. I've yet to meet a piece of crud big enough to stop the buffer. It may feel/sound a little rougher to the hand and ear, but it will work.
And yes, wet bolt not a wet weapon. I can't believe how much oil some people use on their AR's

