Uuum, yes, Juugo is a sage!!! He uses sennin trasnformation, also know as curse seal, thus transforms into a sage... This was confirmed like 50 chapters ago, where have you been?
Its a transformation but that doesn't mean he is a sage. His ability is a body manipulation ability that enhances existing features. A sage mode is enhanced in a very different way. In addition juugo as we have seen in the past relies on his own chakra instead of sage energy gathering. His curse seals he helped create optimize a person's existing abilities enhancing them to their maximum potential. Sasuke while he had the curse seal didn't have sage chakra nor did he ever gather it. His seal like all the others allowed him to use his full potential early instead of waiting for his body to naturally reach that level. Sage energy on the other hand allows outside energy from all living things to enter the body enhancing it with abilities uncommon of what it had before. While they may seem vaguely similar they are very very different.
Oh and by the way he is referring to kabuto's transformation idiot. Look in the picture and you can see kabuto in sage mode.
As far as orochimaru combining with sasuke, that won't happen either since orochimaru has just taken a zetsu body for a host nor can he simply jump from one body to the next at a whim. It takes time for him to jump from one body to another which is why he can't automatically just merge with sasuke.