What about older developers who worked before Github and so had their own projects dissolved to obscurity?
What about developers who don't do side projects but give 120% to the company product, even at home? (Some of us actually enjoy working on the products we build during the day :D )
You'll get exactly the same mileage by just asking the potential hire to tell you about something they built - full stop. You'll be able to gauge passion, if they actually did the work, how it solves a problem. You just won't be able to play with it, but I suspect the minimum of side projects is in any case live, and more about scratching an itch.
And even with non-disclosure agreements etc they'll be able to tell you enough of the technology to be able to make a call.