While arbitrage is forbidden, placing AdWords ads on the pages that have value and purpose other than serving ads and simultaneously buying AdWords traffic is legitimate.
Jacques is correct here, if the ads on the landing page are substantially similar to the ad word buy then Google will penalize you. So if you buy and Ad for 'hair dryer' and you have a page which says "a hair dryer drys your hair." and a bunch more AdSense ads around it for buying a hair dryer from different vendors, that will eventually get you in trouble.
It is however "ok" to buy an adword to a page about, say a '65 mustang restoration article you did. Have it be mostly an article about restoring a mustang and a "few" (for some opaque definition of a few) AdSense ads on the page which may or may not be related to the AdWords buy.
But what is really the bottom line is that the variations are endless :-)
Then you're asking for trouble. Some google flunkey will have to determine what 'value' is, come down on the wrong side of your imaginary line and boom gone is your adsense account.
It's a risk some are willing to take but I would be very careful with that strategy, especially if the pages are used in this combination right from day 1.
It is however "ok" to buy an adword to a page about, say a '65 mustang restoration article you did. Have it be mostly an article about restoring a mustang and a "few" (for some opaque definition of a few) AdSense ads on the page which may or may not be related to the AdWords buy.
But what is really the bottom line is that the variations are endless :-)