The HiHy is definitely different underneath. I've been looking into side steps. Distribution of the OEM (Steel Horse) step was halted by toyota. I still haven't found out why.
I spoke with a local manufacturer
http://www.thoffroad.com/toyota/highlander/index.html and they said they've been having issues with the differences of the hybrid in regards to the side steps.
As for bumper coverage, they do make a nice rear pipe bumper that attaches where the shipping anchors are in the rear. Front I dunno. You might want to give them a call.
I personally have the "clear bra" stuff on my front and rear. I didn't want the weight and don't like the bull bars.