If you look into the history of Hapkido, you'll see the founder supposedly studied Daito-Ryu Aikijujitsu with Takeda (so shares those roots with Aikido) and that Hapkido is a korean version of Daito-Ryu. I vaguely remember their is some controversy about this, that there is some doubt about whether a Korean would have been allowed to study with Takeda at the time and I don't think his name appears on a roll, so I say supposedly but I think the roots seem to be obviously there somehow. I could be corrected about that
Equivalent Aikido forms in the video, I'd say: the first looks like sankyo and then kote geashi and finally something like a shiho nage variation. Later is sankyo again and kote geashi with the gun.
As for guns, I've never trained gun disarming in Australia, but in the USA, with guns more common, I have done a little here. Remember though you may train tanto, sword and jo disarming in the dojo, but this could easily be a broken bottle, lump of wood or bar stool, any weapon from a few inches to a few feet long really. I had one sensei tell me that in his Shodan tests, his sensei was feeling particularly adventurous and bought out a shotgun and made him do disarming techniques, unloaded of course ... I hope
Want some real fun, if you have a naginata handy try doing some disarming, naginata dori, with that. Talk about adjusting your ma-ai and irimi!