Short answer, yes simply because 6.5 is smaller than 30 caliber. Things to also consider for the sake of information are barrel length restrictions due to higher muzzle pressures, and silencer weight. TBAC Ultras will be one of the lightest and best at sound reduction, as well as precision. TBAC length restrictions are very respectable, I believe you can find them on the product pages for the Ultra models on their website.
Usually a silencer with a bore above the caliber of the bullet will grant a lesser degree of sound suppression vs a can with a equal caliber specified bore, but in most cases this is pretty much only something you can tell by literally metering them with properly sensitive sound measurement devices. With the TBAC Ultra cans comparing the 6.5 through 30 cal vs 6.5 through a 6.5 can I think it's something like one or two decibels difference. So does it make a difference, really? Not really.