>>27752461Their Pokedex entries on the JP site seem to indicate that they are available. Outside that we've seen two Team Skull members use Zubat and Golbat, we know they are catch able.
Dragonite's dex says something about an island full of them and is pretty much tied to Alola instead of general like it was before.
As for why the other three aren't listed, they probably didn't want to list them. We know Pikachu is catch able since Hau has a Pichu and Kiawi's Marowak hints that Cubone is catchable. Since those three have representation through their evolutions, they probably didn't feel the need to include them.
The title above Dragonite and Zubat is "Pokemon that have been found so far." So these are the first they decided to show us are available in Alola without having an Alolan Variant form.
The non-sunmoon jp pokemon site's news block for Zubat and Dragonite says:
To "Pokemon Sun Moon" , also appeared Kairyu and Zubatto!
(Good god that translation butchering.)
From what I can make out of the statement:
『ポケモン サン・ムーン』に、あのカイリューとズバットも登場!
"In Pokemon Sun and Moon, Dragonite and Zubat also appear!"
I'm a complete amateur at this and using a translation dictionary and Google. Didn't know where to place the "in" cause it stood out but was really out of place appearing after Pokemon Sun Moon. The "in" also translated to "to" just like it did above, but I had another word added in "that". So it read In Pokemon Sun Moon, that Dragonite and Zubat also appeared!
Every translation I tried makes it sound as if they are saying that Dragonite and Zubat are available in Alola. Since they are being used separate from Alolan Variants, they appear normally (and we've seen trainers using normal Zubat and Golbat). Dragonite is an oddity since it's being paired with Zubat, but these were the two they chose. They have what ever reason they have for using these two.