The article is full of interesting
examples of linguistics differences between NK and SK, but…
As someone with a degree in linguistics, I question whether the author of this article has a sufficient grasp on the subject to put it in proper context.
One of the clearest indications of a superficial understanding of the subject matter is in the section describing "words with different meaning but the same spelling" or "homophones." The examples given are word pairs like "service" and "volunteers," which are obviously related in meaning; these are what linguists would immediately identify as examples of semantic shift (or perhaps polysemy), not of homophony.
Basically every language with more than a few thousand speakers in close proximity has internal dialectical differences. Americans and Brits experience linguistic difficulties similar to what's described in the article ("nappy"…?) when newly-exposed to each others' English. Having lived in various parts of the US and Canada, I know that the same thing happens even among people without easily distinguishable accents.
Judgments and assumptions about other subgroups’ use of language is also pretty universal. Stereotypical Southern accents are often perceived as uneducated in the northeast and west of the US; Québec French is perceived as degraded by the influence of English in France, although in some ways it's extremely conservative (in the linguistic sense) and retains words and other features of 18th-century French.
Anyway, this is all to say that the article is interesting, but the linguistic barriers it describes are unsurprising and not in any way unique to Korea. Without a more informed take on the subject, I'm skeptical that language differences are such a huge barrier to integration of North Koreans into SK society, any more than a British or Australian is Nigerian accent is a barrier to integration into (say) Seattle or Vancouver.