The previous iPad Pros didn't say anything about HDR in their specs either, yet were able to download what Apple calls HDR versions of iTunes videos, Netflix added HDR streaming, etc. I can't see why the new Pros would have downgraded this capability.
I believe the version of HDR that iPads support is pseudo-HDR, which is probably why it's not being bragged about. They don't meet the technical contrast and brightness constraints of the HDR10 format, which I believe is what the HDR TVs support.