With Templar, as long as the vow is taken, even if the champion is alive or zzapped by Zag, the vow stands, unfortunatly.
About the neophytes- not entirely true. If he takes a Chaplain- the templar's other favorite HQ choice- everyone in the party, even neophytes who normally can't, can re-roll failed hits.
And to clear it up, he rerolls all FAILED rolls. It really hurts horde orks in that they get so many hits, and with the average boy's statline, it can really give them a bruising. What I'd reccomend is Nobs with hidden claws, those can really Tear into Templar. Deny them the charge, as well, and try to hit him first whenever possible to deny the extra attack, and try to hit him with units with a higher I rating, or he'll just rip and chop again.
No Pity! No Remorse! No Fear!
Black Templars- The Redemption Crusade
Space Marines- The Shadowrunners