I think, if Voxel.net is the one controlling the border routers and routers then they can configure your IPs to do reverse lookups. I don't see any difference in site performance if rDNS is set or not.
In fact, we just set up rDNS on our servers main IP and disable rDNS on virtual IPs. We have to setup rDNS on the main IP of our machines b/c some mail servers will not relay email if there are no rDNS.
We've also noticed that on a Cisco7200s , once you have over /19 IP blocks routed thru it, the routers can no longer do rDNS on the extra IPs over the /19 block limit.*
*I could be wrong though