If the disk tests passed, so all recommended tests at
https://www.hdsentinel.com/faq.php#tests
1) Disk -> Short self test
2) Disk -> Extended self test
3) Disk -> Surface test -> Read test
4) Disk -> Surface test -> Reinitialize disk surface
do not show errors, then yes, the hard disk is safe to use. Then all problems (the one bad sector in this case) already found and corrected: now the spare area is used instead of the original bad sector.
Generally very small amount of bad sectors can be acceptable and usually then the hard disk can be used without problems, as described at
https://www.hdsentinel.com/faq.php#health
but as you can see, even one such reallocation may cause that the hard disk was not responding during the reallocation procedure and then the RAID controller disconnects the hard disk because of a timeout. So this could degrade the array, as you can see.
Ideally all disks should be tested by the above methods before making a RAID array on them, exactly to reveal / stabilize such issues before that could cause a degraded RAID array.
You may re-use in the array but only with constant monitoring to reveal/show possible further issues.