I think radiation unreliability is orthogonal to fixed upper bounds. Radiation is as likely to flip a bit in the check of the upper bound as anywhere else. Having that upper bound hardcoded won't protect against that at all, as far as I can see.
It will ensure a more rapid recovery to a safe state. This is why in principle you don't check for loop termination with "==" when ">=" or <=" will better protect against a corrupted loop counter.
On such a system, would the code execute out of ROM? Or would the ROM image be loaded into RAM? If the latter, then radiation could flip a bit in the code that represents the upper limit of the loop.
Still, if you're going to use words like "better protect" instead of "protect", I'm not sure I can say you're wrong...
RAM and ROM can be nominally protected with ECC, which many rad hard processors provide. It's the internal state of the processor (registers and control logic) which is not fully protected. The inherent hardening of the process makes faults less likely, but they are still guaranteed to happen. There are design approaches to improve reliability with triplicate flip-flops but you pay a power and area penalty. Higher level redundancies aren't always practical also due to mass and volume constraints. At the end of the day software has to account for running on an unreliable system and minimizing bad stuff happening as much as possible.
