The tour to the Humantay Lake is possible to do it from Ollantaytambo, as long as it is in a private tour, if you want to go in a shared group it is almost certain that you will not find that option, the reason is because the route from the city of Cusco to the Humantay Lake is different and has more than 1 hour delay.
The only option to go from Ollantaytambo to the Humantay Lake is on a private tour, ask for rates with us.