To make the obvious point... if voice actors got a cut of sales, wouldn't PSO2 retain the rest and wouldn't that still be more than the nothing they'd get from either distributing them for free or not making them available in the first place?
Perhaps the tricky part is how you register a sale. If they're part of an AC scratch with other items, how do you measure the intent of every player that uses that scratch that the voice tickets were either the only reason they scratched or had nothing to do with it? Or if it was somewhere in between and the voice tickets swayed players into scratching for something else they wanted but otherwise wouldn't have scratched for?
This gets slightly more complicated with SG considering that's ostensibly a freemium currency that is both bought and on a limited basis given for free. Even before considering the split they'd have to work out how to enumerate the real-world value of an SG scratch with that complication.
One way to circumvent all that would be to just sell voice tickets directly for AC, maybe for a period of time in the AC Shop. If the sales cut is then the biggest hurdle they could approach actor/s and/or their agency/ies and open with an offer to share... I don't know, 10%, 30%? Of the income from those direct sales for the use of the combat lines already recorded and used by their partner card and emergency trial instances.