You're right, that is Yoshiki, and there is also Taiji, but he wasn't in Dementia in that time. In that day (17.11.1986), Dementia, X and Saver Tiger played in the same place - Meguro Rokumeikan. It was first time when Taiji played with X ( and Kerry from Mein Kampf was on guitar ). And in the end of that gig all three bands played God Save The Queen.
@TheSuicideCityMayor He is; You can see him actually since 1:15 coming from backstage and in 1:42 he jumps into the crowd just in the moment you're saying xD