SSD Software RAID Alignment Necessary?

It is not necessary, everything will work and probably still much faster than spinning metal based drives, but better alignment will further improve performance particularly for write operations.

Newer installations get this right out of the box automatically (current Debian/Stable certainly does, no doubt newer CentOS variants will too) because recent releases of fdisk, lvm, mdadm, and related tools have been updated to account for best practise on these newer drive technologies, but for older releases you need to set your partitions up more manually to get the best out of your SSDs.

It should be possible to realign in-place but it would be much safer IMO to backup the data on the machine and rebuild - in either case the downtime involved might make this not worth the hassle for you.