Do I need to recreate my TrueNAS pool when switching from non-ECC to ECC RAM?

No, you don’t need to recreate your pool. ECC vs. non-ECC is a memory thing, not a disk format thing—the pool is stored on drives, not in RAM. Just swap the sticks, boot up, and TrueNAS will see the same drives, same zpool, same everything. The only caveat is that if your old non-ECC RAM silently corrupted data in memory before hitting disk, that corruption is already there; switching to ECC won’t fix it but won’t break your pool either.