I have 1Password 3.8.19 installed at home on Lion, using Dropbox sync on my personal Dropbox account. I'm at work, also on Lion, with a Dropbox For Teams account.
I've shared the 1Password.agilekeychain_folder from my home account to my work account, and it's finished syncing to my work Mac under ~/Dropbox. But my 1Password 3.8.19 here doesn't seem to recognize that it's an Agile Keychain; when I use "Find Existing Data File" and click "Open", it just opens the folder like any other folder; see the screen shots.
I managed to get it to recognize the folder by setting the data file directly in Preferences. So it looks like it's just a bug in the installation wizard.