Is that a pretty certain sign the disks are OK?

No, not certain. It does mean that the disks are not having trouble right now. But if it's an intermittent problem like a loose solder joint, then the problem might come back later.

(I.e. is it equivalent to performing a surface scan or similar?)

No, it just makes sure the file links and the sector allocations are OK. In other words, it checks the file data to make sure it's OK, not the disk hardware reliability.