When I play Sacrifice to kill my Glasc Mixologist to play Vanguard Captain - will it enable its Legion to play 2 recruit tokens?

Yes — Sacrifice enables Vanguard Captain's Legion, so you get the two 1[M] Recruit tokens.

Legion checks whether a different card has been finalized by you this turn (Rule 812.1.c), and Sacrifice was finalized when you played it — before Glasc Mixologist's Deathknell even resolves. So when the Deathknell plays Vanguard Captain from your trash, Legion is already active and its "When you play me" makes both Recruit tokens at the location Vanguard Captain entered. It doesn't matter that Sacrifice is still resolving on the chain; even a countered card would satisfy Legion (Rule 419.4.b).