It is not. PCCW and HE are simply too well peered for IPv6, not a lot flows inbound via Cogent.On my random test, I also noticed cloudshards , but it doesn't have cogent+HE on ipv6 if I saw it right (AS62638 - cogent missing on ipv6)
BGP routing table entry for 2602:FFE8:300::/40, version 110148281
Paths: (1 available, best #1, table Default)
62638
2001:550:0:1000::421C:127 (metric 10166061) from 2001:550:0:1000::9A36:424C (154.54.66.76)
Origin IGP, localpref 130, valid, internal, best
Community: 174:3001 174:10017 174:20999 174:21001 174:22013
Originator: 66.28.1.39, Cluster list: 154.54.66.76, 66.28.1.69, 66.28.1.103, 66.28.1.9, 66.28.1.68
Not appearing on the IPv6 peer list doesn't mean they don't have Cogent. HE relies on BGP table feeds from other networks to build their data, and they just don't happen to have a BGP feed from someone that has primarily Cogent on IPv6, which is understandable since I'd say every other network relies on HE for IPv6.I don't have good networking knowledge, but I didn't see 'cogent' on ipv6 for AS62638
HE+cogent on both v4 & v6 is the requirement
image link below: (could not attach image, dialog doesn't close)
http://s11.postimg.org/vrkq1u1dv/as62638.png