I haven't used Alarms, but in case it's helpful, OmniFocus includes built in Growl support. Looks like they updated their API for the most recent 1.3 release (we'll update OmniFocus to support it) but previous versions should work fine as well.
OmniFocus also includes the ability to *export* information about your deadlines to a file that iCal can read information from as part of the sync process. Check
this post for more info. Does that work for your purposes?