When RH was written, Orc Boyz and Arrer Boyz were a single entry. The errata released in WD after the O&G book was released said that CDs could take both (the full text is in the Direwolf FAQ). Goblin wolfriders have never been allowed. No reason you can’t use the models though.
WD250 included errata on how to use CD with the new O&G army book, which explicitly permits the use of Arrer Boyz. However, since Arrer boyz are not listed in RH you might have trouble convincing some people to allow them, but that should not be a problem in friendly games.
I’m going to try to play CD in 'Ard Boyz, but don’t plan to use any Arrer Boyz just to avoid this issue just in case there is no FAQ released which clarifies that they are allowed.
Why would you need them at all ? - hobgobs with bows cost 5p
Arrer Boyzs are just 1 point more which pays for their light armour. In addition, they have toughness 4, leadership 7, and the choppa rule. If you are playing a battle that has a building then you'll want to put Arrer Boyz in it if you have the special slot available. If you're not sure why Arrer Boyz are better than Hobgoblins in a building then look over the building special rules regarding who wins combat and what happens to the loser (or if there is a tie).
If that building is 2 or 3 stories high you might want to go with Blunderbusses as they get +1 strength for each storey that 5 models can shoot out of (per the GW FAQ).