The ratgeber (advice booklet) on Pillar 3a says this pillar is not available to housewives (or housemen). I take that to mean Goldtop is right, in other words if you have no income at all in a year, you cannot contribute. You are also asked if you open an account whether you are employed and contribute to a pensionskasse. So regardless of whether one is part of a couple, I think with pillar 3a only the individual situation counts.

Interesting though that you can contribute if on unemployment benefits. I guess those are taxed and you pay AHV so it makes some sense...