I highly doubt Kenshin would have done what Nobunaga dide, especially at Hiei. But it is impossible to tell at this point. The reason I do not believe that Kenshin would have committed such acts is that when he was 14 his older brother was in charge of the clan (forgot the name, the one Kenshin was first a part of)., Kenshin was encouraged to depose his brother and was offerred the services of many of his father's vasals. He eventually decided to help, but only because his brother was abusing the people and ruining the clan.

I think Kenshin and Shingen were both much more benevolent rulers than Nobunaga.