The werewolf shapechange ability states that it polymorphs into a wolf. Does that mean it gains pack tactics as an ability in wolf form?
No. The abilities the werewolf has in each form are listed in its stat block. From its Shapechanger ability: "Its statistics, other than its AC, are the same in each form," where statistics would include pack tactics.
RAW: All monsters only have the abilities as listed in their stat block. As werewolves do not list "Pack Tactics" as one of their abilities, they do not get it.
Otherwise: There is nothing preventing a DM from homebrewing an exception to this rule. That said, if you do, you should fairly adjust the stats of the encounter (including CR) to adequately reflect this additional ability.
Ultimately: While it is best to follow the RAW when possible, sometimes you need something special and different to better fit your campaign. Don't be afraid to mix things up and create your own versions of monsters, just be sure to have an in-universe explanation ready in case it gets challenged by the players.
RAW, no. The stat block does not include that in any of the shapes.
Rule of cool, rules that make sense, RAF, I'd say they should, and I will be so running that way in the future. Likewise, weretigers getting pounce, wereboars getting to charge, etc. (when in full animal form).