Companies do not typically throw "red herrings" into an ad just to see if an applicant notices. In fact, most employers would wonder about an applicant who sends in a resume along with a red-penciled copy of their job advertisement. In many cases, the next thing to be red-penciled would be the applicant.
However, much of this depends upon the company and the way that you present the corrections. There are people in some companies who may think that an applicant who has the confidence and expertise to correct their advertisement may be just what the place needs. But, other individuals may think that such an applicant is overly critical and may be real trouble. You need to check out the companies carefully and tailor your presentation from there.
The odds are that correcting an ad is more likely to work against you than for you. With this in mind, the safest approach is to let your resume and cover letter initially demonstrate how thorough, accurate, and detail minded you are. If you get to the interview stage, then you may consider mentioning the company's advertisement. Be sure to do so in an upbeat, non-evaluative, and constructive tone. And, you better be right!
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