Hey Rod, I can't check it right now because I don't have the docs here or access to a Spectrum install, but I think they did work the option for html content into probable cause files starting somewhere in the 9.x Spectrum version. You could try a quick search in the docs (if it's documented, it could just be buried in previous release notes) or just give it a try.
Like I said before, I'm not sure if the web context url is user writable. They might simply point it out so it is easy to use when building event format files and you want to include the url the device provides (usually the link to the management web interface). As far as I know there is no update alarm (CLI) command to set the web context url. The only updates you can do to add text is the status and ticket. So you could use the ticket field for this if you don't have any other plans with it. If you want to refer to a wiki page for example, you can fix the standard url in OneClick (have a look in your preferences) to something like "http://wiki.company.com/" and then add the pagename in the ticket field to complete the url. You can set the ticket with a script through the command line interface using a command like "update alarm -r aid=1234 ticket='AlarmInfo'". I haven't tested it,since I have no docs or Spectrum here now, but I think this should work.
Hope that helps,
Michiel