How come some "actors" (?) are only credited with voice dubbing but have no any acting credit still considered beeing actors - such as
http://hkmdb.com/db/people/view.mhtml?i ... ay_set=eng or http://hkmdb.com/db/people/view.mhtml?i ... ay_set=eng ?

Dubbers are actors. If you search for animation film entries at the IMDb, you will see they are listed as actors, too.