The aptly-named Love Time Hotel in Rio, in Copa across from the Gloria metro station, and right around the corner from Club 117, the games garoto sauna, is probably your best bet in Rio. It's known for and marketed to adults going for hookups or "romantic getaways", the security is goid and the rooms are not that shabby. I believe they may only require local guests to be signed in by the hotel guest with their Brazilian ID -- if that at all. They do require anyone staying at the hotel not accompanied by the hotel guest to call up from the front desk before they are allowed to go up -- or the guest may have to go down to the front desk to sign them in. I have never had a problem.
In Sampa, I recommend Bourbon São Paulo Express Business Hotel, in República, which is one block from the Republica metro station and in or around a somewhat active but low-budget gay scene, and in an area of the city with a lot of business and pleasure activity (but as always, be cautious where you venture). The hotel has never minded much when I bring back a guest, and has even sent pay boys / escorts up to my room without first having to announce them or sign them in.
Good luck and as always, use common sense and good judgment.