I recently picked up a Super 14 Match Grade .22 LR Contender Barrel. This is a factory barrel, to say I am pleased with it's accuracy would be an understatement.
Yes the chambers in Match Barrels are cut to tighter specs than are standard sporting chambers. In my barrel the bullets engage the rifling.
This barrel also seems to shoot a lot of different types of ammo good, but shoots certain brands and types great.
As to the shooting of High Velocity .22 LR Ammo in a Match Chamber, the reference should be for Hyper Velocity Ammo in a Match Chamber. Certain brands and types of HYPER VELOCITY .22 LR Ammo do indeed use a cartridge case that is longer than standard, and could damage a Match Chamber. Cartridges that come to mind are the CCI Stingers, Quick Shok, and maybe a few others I can not think of right now.
I can not say for sure if the Match Chamber is worth the extra $$$, I have never owned a standard .22 LR Contender Barrel. However as with centerfire guns and chambers, the chamber can and does make a difference in accuracy.
Larry