Why not? For HDR you need two things: high bit depth and a transfer function to match. H.264 supports both 10-bit video and at the very least the Hybrid-Log Gamma function. H.264 also supports the Rec.2020 wide gamut colour space so I don't see why it wouldn't support the PQ curve as well. So I think HDR10 is also supported.
Very few H264 decoders can decode those profiles. Basically anything other than Baseline, Main and High is going to be pretty hard to find. Hi10p, Hi422p, etc. are very uncommon in hardware decoders (no iPhone or Core i7 processors supports these).
That leaves software decode, which is pretty hard on phones and other constrained devices.
Can't you take that kind of HDR H.264 video and then convert it to baseline H.264 compressing the palette intelligently so it would look not exactly like original yet still very much alike with everything significant easily distinguishable visually?
But at the very least HLG works on H.264.