I mean, it sounds like a win-win situation to me. If a family can save, say, $3,000 a month on rent, and the company can save, say, $1,500 on an engineers salary, both are actually better off.
I guess the risk of moving out of the Bay Area is that you somehow are betting your future on a single company. If you decide to get a new job, you might be too far away from a decent tech hub. Another issue for families is moving both working partners. If the partner works at a company that might not be as flexible or open, moving somewhere else is going to be a tough decision, as it's always going to be better to have 2 jobs in the Bay Area, than just one outside of it.