I'll be there; I manage my company's corporate hospitality at Olympics, so it'll be work. Hotels are currently a major issue. As background, the IOC asks hotels to submit what #/% of their rooms they are willing to allocate to Olympic-related organizations (NOCs, Federations, sponsors, etc.); the deal is the hotels are not supposed to gouge on the room rate.Then these organizations request their required # rooms at whichever hotels strike their fancy. The IOC then confirms how many rooms each organization has been allocated where. This step occurred in June 2014. So the majority of rooms have already been snapped up by the Olympic "family". These organizations, however, have to confirm/commit to their rooms on July 1, 2015, so there may be inventory coming back into the market next month.
(In general, anything a hotel did not sell-off to one of these organizations were then sold to a consolidator who packages the rooms with tickets, etc and then charges 10x their cost.)
As Rio has relatively few "business class" hotels to start with, you're going to find that the vast majority of rooms have been allocated as above. What you may be successful in finding are rooms during specific dates (for example, I'm hearing of availability the last week of the Olympics as teams that have competed in the first two weeks head home vs "staying around" as they normally do).