It is INDIGO, not INDI, framework inside APT. INDI support is only a side effect of a partial INDIGO backward compatibility and only to a limited extent, e. g. fall-down to legacy INDI protocol including INDI BLOB support and formally documented INDI property/item names mapping. INDIGO doesn't and probably never will support legacy INDI streaming and snooping because a different approach was taken already.
As far as INDI has no documented DSLR properties in addition to the common CCD property set, gphoto2 INDI driver is not fully compatible with INDIGO client on properties/items level, because no name mapping does exist. Nevertheless, it may work on some very basic level (trigger the capture in M mode and download image).