I don't think Dolby Headphone is dependent on the Dolby Digital/AC-3 codec specifically, as that would be far too limiting, but that it just needs a 5.1 or 7.1 source of any kind to work, be it Dolby Digital, DTS, Dolby TrueHD, DTS-Master Audio, LPCM, analog, or even a properly decoded Dolby Pro Logic II signal. The source signal gets decoded into its component channels first, then the DH processing is applied.
It just so happens that most 5.1 sources are encoded in Dolby Digital to begin with, especially console games on the original Xbox and beyond, likely because of a Dolby Digital Live-esque tech being included by default. (Now if they'd just mix them straight into HRTF, like a binaural mix...)
If you use DH via a PC sound card or an A/V receiver with HDMI, like those older Harmon Kardon models, you would most likely get virtual 7.1, not just virtual 5.1, using the same basic HRTF mixing methods.
The fat PS3s can't bitstream Dolby TrueHD or DTS-Master Audio over HDMI, but they're perfectly capable of bitstreaming Dolby Digital and DTS over S/PDIF. (Probably HDMI too, but it's not strictly necessary because HDMI has the bandwidth for 7.1 LPCM, which is already superior in quality due to being lossless.) Otherwise, it would be in the same precarious position the Wii U is regarding effectively getting discrete surround sound signals (not matrixed ones like Dolby Pro Logic II) out of the console and into a headphone surround processor.
I'd still rather have the near-complete PS2 compatibility of the CECHA over the HDMI bitstreaming of the slim PS3s. Too many PS2 exclusives I missed out on last time, and I don't even have any A/V receivers with HDMI inputs, let alone loudspeakers to connect to them that would make the higher-end formats audibly superior.