Yahoo pipes feed is not validated by so many resources like feedburner, magpie, lylina etc.,
Why are you not validating it from your end?
What do you mean?
yahoo pipes feeds are standard rss feeds, so there should be no validation problems. And if there is, pipes should thus not be the source of the trouble, and you should look/point the finger at the resource you talk about instead, should you not?
Can you provide your Pipe that isn't validating?