Just a bit of an update on this. I stopped by my LDS yesterday, and noticed they had a QR code displayed that customers could use to verify their dives. I'd never done this, so was curious, and started to look into it.
Basically, when you scan that QR code, it uses the SSI app (or maybe the SSI website) and identifies dives that haven't been verified. So, I went to my SSI account, and looked at the logbook. I was mainly looking to see if there was a way to import a .csv file or something. There isn't, so at first glance, it looked like it was only really going to be useful for divers using Mares computers. Then I noticed a menu option below the logbook.
It said "Import Dives (Beta Access)", so I was intrigued. Turns out they are opening it up to Garmin users (via Garmin Connect) now as well as Mares. I was able to successfully import the dives done with my Garmin computer. I still don't think it's nearly as useful as other dive logging software, but if you want to have your verified dives match your actual, for whatever reason, it does work.
One thing I really don't like about it. In order to add a dive to the log (manual or via Garmin computer) you need to select a dive site. It needs to be a site that is in the SSI database, so in the cases where it didn't recognize my dive sites, I had to use something else. There appears to be a way to add them, but I'm not sure how, and didn't really care to dig into that level.
Long story short, the SSI app now allows importing from Garmin computers as well as Mares, so a step in the right direction.