Chapter 11.5.4.1 "Invoking an Action" reads:
"...
To request processing of the action only if the binding parameter value, an entity or collection of entities, is unmodified, the client includes the If-Match header with the latest known ETag value for the entity or collection of entities. The ETag value for a collection as a whole is transported in the ETag header of a collection response.
..."

--> We support ETags for collections via the standart ETag Header.

Looking at the chapter 8.3.1 "Header ETag" we never mentioned collections; we described the usage of ETags for metadata responses, service document reponses and for requests that returns an "individual resource".
The formulation "individual resource" is fuzzy and needs to be clarified.