|You can indeed replace the "?" with a "!", so "!openform" works just the same.|
Look in your server document, Internet protocols tab -> Domino Web engine -> Make this site accessible to Web search crawlers, Enabled. This will cause Domino to generate ! instead of ?
Many of the ? URL commands are implied anyway, so you can build your Web apps almost without using any.
Also, remember that search engines are not very effective these days, so don't expect a good return even when you do get everything right on your server.