You can't detect whether a URL handler worked correctly in a browser; otherwise Windows will appear with a "Select an app to open YOURPROTOCOLHERE://" which is completely nonsensical to the user.

As for option 2; ask them every time, or edit their hosts file. Easiest decision in the world: Edit their hosts file, every time, no question. The 1% of nerds who care, and oddly enough don't buy Adobe software, are completely meaningless to the 99% of customers who experience the decision positively.