I had this conversation with the club early on in City Matters. They openly sell tickets to various official partner agencies for home games. However there were agencies who weren't official partners openly offering packages and I pointed this out to them.
I have severe doubts that the club is directly involved in supplying third-party sites with away tickets on a large scale, as these sites mostly operate on the wrong side of the law. But if they are supplying any of these sites, then it has to be out of their 5% ticket allocation, rather than the season ticket holders'.
It's far more likely that these sites have access to tickets via hospitality season ticket holders or those with high points. I've heard anecdotal evidence of people paying for their hospitality season tickets via this sort of activity.
Hopefully the Ticketing Compliance Manager will be able to make some inroads into this. Just buy a couple of tickets and see where they came from.