ZeroAccess cannot be considered as RAT as none of it features or plugins not providing remote administration support. From the beginning RAT is not malware (e.g. Radmin/RealVNC), but a component that can be used by malware, while backdoor is a malware with implemented minumum remote administration functional as a optional feature.
Some trojans with backdoor functionality positioning itself as RAT, for example Blackshades. In the same time they offer crypter for their "product" ("prevent others (no matter who) from analyzing your executables (EXE) files") and multiscanner - "scanning engine to determine which anti-viruses detect a file". Making itself look legitimate as only possible.
Ring0 - the source of inspiration
