It definitely happens in the valley; Cisco was notorious in the 90s and 00s for acquiring "spin-ins" (startups founded by ex-Cisco leadership/teams with an almost certain expectation of returning to the mothership), and I'm sure there are other examples.

Less drastically, Google (and I'm sure many other valley peers) will often set up special incentive structures for certain teams: bonuses tied to aggressive adoption metrics and separated from the company-wide bonus, for example. I doubt it comes close to cutting that safety net (and making people truly hungry), but I give them credit for trying.