I have seen reference in the literature to the fact than nominate dasypus may lack black below the bill. However, I have not seen this any of the dasypus I have trapped (in HK and on the breeding grounds) or on skins I have examined so I'm not entirely convinced on this. That said nigrimentalis consistently exhibits more black below the bill than nominate (John's final image is a classic nigrimentalis). In terms of the extent of the white rump, it is worth noting that in the subspecies of Northern HM which breeds in NW China (and hence could occur in HK) the longest upppertail coverts are black rather than white (= lagopodum) and as such has a rump patch similar to that of nominate dasypus, however, that subspecies has a very deeply forked tail which should be obvious in the field.
The bird in the link provided by Brenden is probably Northern based on large body size, lack of black below bill and clean white underparts, but without information on rump pattern and tail structure I don't think it can id'd with any certainty.
