A balaclava with no UPF rating can work just fine depending on when and where you ski. If you mostly ski on overcast days, hit night sessions, or plan to wear it layered under a helmet and goggles that already shield your face, the lack of UV protection won't be an issue.
The catch is that UV exposure at altitude is significantly stronger, and snow reflects up to 80% of UV radiation right back at your face. So on sunny days at higher elevations, an unrated balaclava may let more UV through than you'd expect—especially if the fabric stretches or gets wet, which can reduce whatever natural protection the material offers.
If you go with an unrated option, just be diligent about applying sunscreen to any exposed skin, particularly around your nose, cheeks, and neck. For spring skiing, high-altitude trips, or if you have fair or sun-sensitive skin, a UPF-rated balaclava is worth the upgrade for peace of mind.