The user has the capability of merging events to multiple calendars. There are two ways to access advanced settings. The first is via the Add-on menu. Select Event-o-Matic >More< Enable Advanced Features. The second way is via Setup. Click on the Letter A with a checkmark on the top bar. You can tell if advanced settings are enabled: if the icon is green, you’re ready to rock!
An additional step is added during the configuration process. The merge on form submit will create an event every time a form submission is received.