One question to think about is: what is the actual incidence of "informed consumer" association between the hard-hatted elephant head logo with Cloudera? I.e. was it really downloaded by a fair number of users, and was it used in an obvious way on the Cloudera website for a notable period of time?
The fundamental question from the trademarks@ point of view is the likely association in the minds of normal users and consumers of our software, not those of us already familiar with Hadoop.
That being said, a logo also needs to fit with the community, so if its causing this much controversy, then from the community health point of view... just pick something else.
Design choice is clearly up to the PMC. From the trademarks@ point of view, the Powered By logo should certainly echo the Hadoop product logo, but have a clear overlay or change to the logo to also make it clearly distinct from the main logo is important. We don't particularly need to have a feather in the logo, but it's OK to add it if the PMC really wants to.
Personally, I'd suggest style-wise something that features more of the whole Hadoop elephant than just the head: maybe the elephant pushing something, or looking through a frame, or something like that.
Note that coming up with a couple of different formats for use in different styles is highly recommended.