Thanks for the quick answer! This is a bug in OwnCloud, it seems. Not an issue with DAVdroid.
The VCard is indeed 3.0.
In the above example, the address type is ADR;UNKNOWN=X-GPS. In OwnCloud, if I change that address to one of the default options (ADR;TYPE=HOME or ADR;TYPE=OTHER or ADR;TYPE=WORK) and then take a look at the VCard, it has an escaped comma like it is supposed to. After that, everything on the DAVdroid end works correctly.
I will mention this to the OwnCloud people. Thanks again for your help! Wonderful.