Hopefully Hashfast's customers won't want to scam each other, so the fears of that may be overblown.
It's far from overblown IMHO. Do you know how easy is to compose an email with a GIF inside with link to a server which will log that email's IP address at the very moment you open that email to read it?
Real IP addresses of confirmed high-amount BTC owners are godsend for all kinds of port-scanning, router and firewall attacks, etc. If this doesn't turn in hundreds (or thousands) of BTC in steals and loses I would be very surprised.