I can't see how...
...people quitting to join an up-and-comer is "suspicious" in any way. Pure has tapped into the EMC resource pool and is likely making very attractive offers in their quest to push their platform to the next level. No big deal. The only reason it's suspicious is likely because these people are intimately familiar with EMC operations and possibly engineering as well, but you can't really "unlearn" anything. Some of those staff might see an opportunity to evolve the Flash Array product into what they envisioned for, say, VMAX, but can't/won't materialize for one reason or another. This is their clean slate. That's exciting stuff for established engineers.
There is a HUGE problem with EMCers taking EMC-confidential information with them on their way out the door, however. Not only is that almost definitely sue-into-the-ground worthy but some of that could be, oh I dunno, MY personal data. Yeah, I have a problem with that.