Alas there is still abnormally high traffic on the hpHosts server. I've been keeping an eye on the server logs over the past few months, and it is apparent that it's either due to HostsMan users sending extremely frequent requests (as mentioned previously) OR lots of people faking the HostsMan user agent (I spoke to HM's developer some time ago and he pondered whether it could be someone faking the UA aswell).
I'm having the server + gateway re-booted as I write this, and will go through the logs once I've got RD access again.
On the plus side, I've also spoken to the developer of WK (the filter I implemented for the server) and he's advised me on how to resolve the access issues for Free Download Manager users. I'll be sorting this out tomorrow.