If you are out of the magnetosphere, wouldn't your data be subject to way more cosmic ray interference, to the point that its actually a consideration?
Yes. And most server hardware is already at least ECC ram. You may still want some light radiation shielding to prevent the worst, maybe some heavier shielding for solar flares. But beyond that, simple error correction can be baked into the software - ecc the bootloader and filesystem and you are mostly good to go