The short answer is no, generally speaking you couldn't take a joseon scholar and drop him in china and expect him to be able to be understood. He'd have to resort to writing.

Classical chinese script, the written lingua franca of NE asia, and the spoken language of the various countries where it was used needs to be seen independently of each other. This is often difficult to grasp for foreign observers, e.g. english or european language speakers, because when you write something you're writing the sounds of the word whereas with a symbolic language you write a symbol (or combination of) that represent the idea that you're trying to convey.

Emoticons are the easiest way to understand this notion. How do you know that ":)" stands for a smile? It's a symbol that represents the idea of a smiling face to western internet users. Basically you had to memorise it but you can use it independent of the spoken language. Increase the number of symbols to several thousand and you have something that you can begin to use a proper means of communication.

Contemporary observers often had a similar problem in separating the written from the spoken and sometimes misstated that two languages were used. To someone not familiar with the situation that suggested that two languages were spoken (again because of the assumption that the spoken and written languages are related), which was not the case.

In korea the lack of relation between classical chinese and the spoken language is exemplified by "idu". This was a system where the symbols used in classical chinese were used (irrespective of their actual meaning) to represent sounds. An analogy would be drawing a house to write "how" because the spoken word "house" contains the sound you want. Basically a hack (i.e. rough and ready) version of an alphabet that's been replaced by hangeul. For clarity, the term "idu" is used to refer to the specific script used by craftsmen of the joseon period as well as an overarching term referring to all systems to write sound.

Reference - "Missionary contributions toward the revaluation of Hangeul in late nineteenth-century Korea" by David J. Silva.