It's not a violation of WoW's Terms of Use to harass anyone unless it is specifically through Chat. According to the rules, it's perfectly okay to spam someone with guild charters, duels, group/raid invites and indeed the battleground AFK reporting. The only difference is harassment from AFK reporting can't be handled by a UI addon.

Unless a lot of people complain about this type of problem, Blizzard isn't likely to do much about it. Annoying? Quite. Easy for Blizzard to fix? Not particularly. They would first have to adjust the rules to prohibit this type of harassment, and then it'd be handled on a case by case basis, and even then it would probably be difficult to differentiate between an actual AFK report and harassment.

Sucks. Hope it doesn't happen too often