The SIP RFCs only relate to the parts of the system that are using SIP. Asterisk is a back to back user agent, and the bit between them is not SIP. Looking at the source code for app_dial, I see no support for video as early media, although I haven’t checked in enough detail to completely eliminate the possibility that it is handled by catchall code.
I have a feeling that the ARI primitives do support an early media bridge, but I’m no certain of that.
I assume you are talking of media from the doorphone, and the doorphone is the UAC, as, going against the call setup direction would also require early offer SDP (which is the more common case).