Interesting. Didn't know that you could mount the same folder twice with different --view.
Your workaround still doesn't allow the owner of the calendar to see the ToDos in the web client, but for your application that may be fine.
Bug 27613 - Tasks should be integrated into Calendar app suggests that what you're doing will be supported. The initial suggestion in
Bug 30787 - CalDAV vevent collection reports vtodo support when it doesn't would break what you're currently doing, but subsequent comments make clear that it's safe for now.