Now (DAVdroid 1.0), group memberships of the current user are queried for home sets, too. This means that if a user is in the calendar-proxy-{read,write} group (as described in Calendar User Proxy Functionality in CalDAV), those proxied resources should be detected too. Furthermore, this could be used for address books, too, by adding similar groups.
If you’re interested in that, please test it in the beta version.