We have season tickets, and last year sold at least half of them thru Flash Seats, and we never had any problems. We went into our tickets knowing that we wouldn't be able to make a lot of the games (because of kids, jobs, work travel, etc.), and our rep was well aware of that before we bought in. I don't know if the rules are different for partial season ticket holders vs. full, and I also don't know if the Cavs will be monitoring things more closely now that interest in the team has jumped a notch or two. But this is the first I have heard of any limit on sales.
BTW, I would think that the classified section on this site might be a good way to sell some of those tickets you can't use.