Skill Swap fails if either Pokémon has the Ability Wonder Guard, Multitype, Illusion, Stance Change, Schooling, Comatose, Shields Down, Disguise, RKS System, Battle Bond, Power Construct, Ice Face, Gulp Missile, Neutralizing Gas, Zero to Hero, Commander, Protosynthesis, Quark Drive, Orichalcum Pulse, Hadron Engine, or Poison Puppeteer.
Source
No mention of No Guard in there, so yes, you can Skill Swap No Guard.
It should be noted Skill Swapping No Guard in a single battle is pointless, as all moves that both are used by and used on the Pokemon with No Guard will always hit.
Hope this helps!
