External hard drives keep failing
It feels like this is happening a bit too often to blame on "Well
  sometimes ya just get a bad one!", and I'm wondering if I am
  overlooking other factors?


Yes!

Based on what you're doing, your using your drives not as a typical home user but more of a "pro" and you should be getting the hardware to match.  Most consumer (especially the entry level drives) have lower MTBF (Mean Time Between Failures) numbers - higher is better - than their "workstation" or "NAS class" drives.  The higher end models also have longer warranties - typically 3 to 5 years.

There are some additional factors you may wish to consider:


Seagate drives are notoriously unreliable.  WD drives are better, but the really reliable ones are made by HGST.
Look to get a Thunderbolt enclosure, rather than a "consumer grade" USB drives.
Populate your Synology with NAS rated drives.  They are designed to run longer, cooler with greater reliability.



  Could it be an electrical issue? ... All my computer hardware is
  plugged into a couple surge protectors which are in turn plugged into
  a UPS batter backup/surge protector.


A battery backup is also a surge suppressor/protector so daisy-chaining one to the next is not a good idea - you could be creating issues if/when there are surges.  If you must add ports to your battery backup, use a power strip, not a surge protector.

Your Backup Strategy

It sounds like you're off to a good start with your backup strategy.  Here's a few points to consider:


Having RAID is good, but don't depend on it for backup.  RAID is designed to maximize data availability (up time), not be a backup. 
The two USB drives attached to the RAID is a good idea.  However, you should be alternating backups between the two.  One for "odd" days and the other for "even".  This will require you to have to different backup jobs but it ensures your data is backed up to two different locations.  Also, to ensure you don't backup corrupted data....


Don't backup the backup!
Backup the actual data only!

Adding Crashplan is also an excellent idea.  Having this backup your files to an offsite location is a very smart thing to do.  Having a regimented backup workflow will ensure your access to data even if your NAS and both backup drives are inaccessible.