The Intel cards are usually agnostic when it comes to SFPs in my experience, but DAC-cables are a bit of a grey area since there's no standard governing them if I can remember correctly. So if you want to play it safe, buy some 3rd party SFPs for the HP swiches and the name-brand modules for Intel (the Intel modules are cheap enough, but name brand HP modules cost hundreds of dollars per module) and run the whole lot over OM3 fiber instead, it's every so slightly more expensive as the DAC cables. Also, if you haven't bought the X520 cards yet, they can be had with or without SFPs of your choice for the same price.