When transfering data from a hdd with a rellocated sector count-warning, is there anything special to keep in mind?

Yes. Be sure to mark the drive as bad so it does not get reused.

Check for Uncorrectable sector count. As long as that is zero, your reallocated sectors were reallocated without any dataloss.

Modern hdds are designed to reallocate sectors in order to "self-heal" during the warranty period. So reallocated sectors may not spell immediate disaster. Just normal and expected behavior.

If you think the hdd is going bad, avoid writing to it. Only read and rescue your data ASAP.

Remember to make backups of the healthy drives as well.