I highly doubt that a suppressor gives any bullet more velocity.
What I would believe is that a suppressor retains much of the muzzle blast as the bullet exits, so the bullet is less disturbed as it leaves the muzzle.
I wondered about that velocity claim as well, but your idea here has merit. Air gun shooters have been fiddling with "airstrippers" on the muzzle for some time for similar reasons. No idea if they work or not.