The fact that he said "no comment" rather than saying, they aren't used by Delta Force lends as much credence to their being used as not being used.
No, actually that doesn't match my own experience with OPSEC. Usually the standing rule is to decline to comment whether it is in use or not. Knowledge of not using something can be just as compromising as knowledge of using something. Declining to comment as a matter of course just helps keep people guessing, not to mention working as great misdirection.
I'm not doubting that Delta might use Glocks. But that comment from Vickers means nothing.